powerpc: Convert fsl_rstcr_restart to a reset handler

Convert fsl_rstcr_restart into a function to be registered with
register_reset_handler().

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
[scottwood: Converted mvme7100 as well]
Signed-off-by: Scott Wood <oss@buserror.net>