ARM: OMAP: Fix compiler error at pm-debug

Fix compiler error at pm-debug

  CC      arch/arm/mach-omap2/pm-debug.o
In file included from arch/arm/mach-omap2/pm-debug.c:30:
arch/arm/mach-omap2/prm.h: In function `prm_rmw_reg_bits':
arch/arm/mach-omap2/prm.h:107: error: implicit declaration of function `__raw_readl'
arch/arm/mach-omap2/prm.h:110: error: implicit declaration of function `__raw_writel'
arch/arm/mach-omap2/pm-debug.c: In function `serial_wait_tx':
arch/arm/mach-omap2/pm-debug.c:59: error: implicit declaration of function `__raw_readb'
make[1]: *** [arch/arm/mach-omap2/pm-debug.o] Error 1
make: *** [arch/arm/mach-omap2] Error 2

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>