sh: kexec: Register crashk_res

Register crashk_res so that it can be used by kexec-tools
via /proc/iomem.

The crash kernel resource needs to be requested the same as the
other kernel resources due to the fact that it's handled during
the common path for adding new memory ranges, so it's added in to
__add_active_range() with the others. This ensures that the crash
kernel is properly reserved regardless of which memory range it's
placed in.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>