mvebu: fix missing include of common.h in pm.c

The mvebu_pm_suspend_init() is missing a definition, so
include common.h which defines this function into pm.c to
fix the following warning:

arch/arm/mach-mvebu/pm.c:235:12: warning: symbol 'mvebu_pm_suspend_init' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>