armv8: minor fix to comment for enabling SMPEN bit

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 <[email protected]>
CC: Mingkai Hu <[email protected]>
CC: Gong Qianyu <[email protected]>
CC: Mateusz Kulikowski <[email protected]>
CC: Hou Zhiqiang <[email protected]>
CC: York Sun <[email protected]>
CC: Albert Aribaud <[email protected]>
CC: Masahiro Yamada <[email protected]>
Reviewed-by: York Sun <[email protected]>