OMAP3+: sr_device: include pm header

OMAP3+: sr_device: include pm header

omap_enable_smartreflex_on_init is meant to be used by boards
which would like to have SR enabled by default on the platform, while
omap_devinit_smartreflex is used by pm code, the protos are defined
in pm.h. This header should be included to ensure that sr_device
function definitions match the prototypes.

including pm.h fixes the sparse warnings (with CONFIG_OMAP_SMARTREFLEX=y):
arch/arm/mach-omap2/sr_device.c:138:13: warning: symbol 'omap_enable_smartreflex_on_init' was not declared. Should it be static?
arch/arm/mach-omap2/sr_device.c:143:12: warning: symbol 'omap_devinit_smartreflex' was not declared. Should it be static?

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