feat(sgi): enable css implementation of warm reset

Enable the CSS implementation of the warm reset for the rdn2 platform.

In addition to these  changes, fix coding style issues that are not
directly related to the code being introduced in this patch.

Change-Id: I75128d8bbcccbc26cf1e904691c7ef71349c622f
Signed-off-by: Pranav Madhu <pranav.madhu@arm.com>