ARM: OMAP2+: prm44xx: make prm_{save,restore}_context static

The prm_{save,restore}_context functions are not exported
so make them static to avoid the following warnings:

arch/arm/mach-omap2/prm44xx.c:748:6: warning: symbol 'prm_save_context' was not declared. Should it be static?
arch/arm/mach-omap2/prm44xx.c:759:6: warning: symbol 'prm_restore_context' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>