powerpc: Convert relocs_check to a shell script using grep

This runs a bit faster and removes another use of perl from
the kernel build.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-By: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>