Change is consistent with other SOCs and it is in preparation
for adding SOMs. SOC's related files are moved from cpu/ to
mach-imx/<SOC>.

This change is also coherent with the structure in kernel.

Signed-off-by: Stefano Babic <sbabic@denx.de>

CC: Fabio Estevam <fabio.estevam@nxp.com>
CC: Akshay Bhat <akshaybhat@timesys.com>
CC: Ken Lin <Ken.Lin@advantech.com.tw>
CC: Marek Vasut <marek.vasut@gmail.com>
CC: Heiko Schocher <hs@denx.de>
CC: "Sébastien Szymanski" <sebastien.szymanski@armadeus.com>
CC: Christian Gmeiner <christian.gmeiner@gmail.com>
CC: Stefan Roese <sr@denx.de>
CC: Patrick Bruenn <p.bruenn@beckhoff.com>
CC: Troy Kisky <troy.kisky@boundarydevices.com>
CC: Nikita Kiryanov <nikita@compulab.co.il>
CC: Otavio Salvador <otavio@ossystems.com.br>
CC: "Eric Bénard" <eric@eukrea.com>
CC: Jagan Teki <jagan@amarulasolutions.com>
CC: Ye Li <ye.li@nxp.com>
CC: Peng Fan <peng.fan@nxp.com>
CC: Adrian Alonso <adrian.alonso@nxp.com>
CC: Alison Wang <b18965@freescale.com>
CC: Tim Harvey <tharvey@gateworks.com>
CC: Martin Donnelly <martin.donnelly@ge.com>
CC: Marcin Niestroj <m.niestroj@grinn-global.com>
CC: Lukasz Majewski <lukma@denx.de>
CC: Adam Ford <aford173@gmail.com>
CC: "Albert ARIBAUD (3ADEV)" <albert.aribaud@3adev.fr>
CC: Boris Brezillon <boris.brezillon@free-electrons.com>
CC: Soeren Moch <smoch@web.de>
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CC: Wig Cheng <wig.cheng@technexion.com>
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CC: Breno Lima <breno.lima@nxp.com>
CC: Francesco Montefoschi <francesco.montefoschi@udoo.org>
CC: Jaehoon Chung <jh80.chung@samsung.com>
CC: Scott Wood <oss@buserror.net>
CC: Joe Hershberger <joe.hershberger@ni.com>
CC: Anatolij Gustschin <agust@denx.de>
CC: Simon Glass <sjg@chromium.org>
CC: "Andrew F. Davis" <afd@ti.com>
CC: "Łukasz Majewski" <l.majewski@samsung.com>
CC: Patrice Chotard <patrice.chotard@st.com>
CC: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
CC: Hans de Goede <hdegoede@redhat.com>
CC: Masahiro Yamada <yamada.masahiro@socionext.com>
CC: Stephen Warren <swarren@nvidia.com>
CC: Andre Przywara <andre.przywara@arm.com>
CC: "Álvaro Fernández Rojas" <noltari@gmail.com>
CC: York Sun <york.sun@nxp.com>
CC: Xiaoliang Yang <xiaoliang.yang@nxp.com>
CC: Chen-Yu Tsai <wens@csie.org>
CC: George McCollister <george.mccollister@gmail.com>
CC: Sven Ebenfeld <sven.ebenfeld@gmail.com>
CC: Filip Brozovic <fbrozovic@gmail.com>
CC: Petr Kulhavy <brain@jikos.cz>
CC: Eric Nelson <eric@nelint.com>
CC: Bai Ping <ping.bai@nxp.com>
CC: Anson Huang <Anson.Huang@nxp.com>
CC: Sanchayan Maity <maitysanchayan@gmail.com>
CC: Lokesh Vutla <lokeshvutla@ti.com>
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CC: Gary Bisson <gary.bisson@boundarydevices.com>
CC: Alexander Graf <agraf@suse.de>
CC: u-boot@lists.denx.de
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>