ARM: 8910/1: fix missing declartion of module_frob_arch_sections

The module_frob_arch_sections function is missing the header declaration
which is in <linux/moduleloader.h> so include that to fix the following
sparse warning:

arch/arm/kernel/module-plts.c:188:5: warning: symbol 'module_frob_arch_sections' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>