Define a new config "zynqmp_ep" for ZynqMP instead
of xilinx_zynqmp. This defconfig supports all emulation
platforms of ZynqMP. Also renamed TARGET_XILINX_ZYNQMP
to ARCH_ZYNQMP.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>