OMAP2+: TWL: include pm header for init protos

twl_init functions are declared in pm.h and used in pm.c
pm.h header defining the protos need to be included to
ensure that omap_twl.c has consistent function definition.
This fixes sparse warning:
arch/arm/mach-omap2/omap_twl.c:237:12: warning: symbol 'omap4_twl_init' was not declared. Should it be static?
arch/arm/mach-omap2/omap_twl.c:256:12: warning: symbol 'omap3_twl_init' was not declared. Should it be static?

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>

arch/arm/mach-omap2/omap_twl.c

@@ -20,6 +20,8 @@
 
 #include <plat/voltage.h>
 
+#include "pm.h"
+
 #define OMAP3_SRI2C_SLAVE_ADDR		0x12
 #define OMAP3_VDD_MPU_SR_CONTROL_REG	0x00
 #define OMAP3_VDD_CORE_SR_CONTROL_REG	0x01