armv8: minor fix to comment for enabling SMPEN bit

The SMPEN bit is located in the cpuectlr_el1 register and not the
cpuactlr_el1 register. Adjust the comment accordingly and also fix
a spelling error.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
CC: Mingkai Hu <mingkai.hu@nxp.com>
CC: Gong Qianyu <Qianyu.Gong@nxp.com>
CC: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
CC: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
CC: York Sun <york.sun@nxp.com>
CC: Albert Aribaud <albert.u.boot@aribaud.net>
CC: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: York Sun <york.sun@nxp.com>