kexec_file,x86,powerpc: factor out kexec_file_ops functions

kexec_file,x86,powerpc: factor out kexec_file_ops functions

As arch_kexec_kernel_image_{probe,load}(),
arch_kimage_file_post_load_cleanup() and arch_kexec_kernel_verify_sig()
are almost duplicated among architectures, they can be commonalized with
an architecture-defined kexec_file_ops array.  So let's factor them out.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: AKASHI Takahiro <[email protected]>
Acked-by: Dave Young <[email protected]>
Tested-by: Dave Young <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Thiago Jung Bauermann <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>