ARM: OMAP2+: sparse: add missing function declarations

omap3xxx_restart() and omap44xx_restart() are global
functions declared in common.h. Include this file
in omap3-restart.c and omap4-restart.c to prevent
sparse warnings of type:

arch/arm/mach-omap2/omap4-restart.c:22:6: warning: symbol 'omap44xx_restart' was not declared. Should it be static?

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Reviewed-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>