Select POWER_SUPPLY from POWER_AVS_OMAP entry in Kconfig.

This avoids the following build problems using a randconfig
that has CONFIG_POWER_SUPPLY not set:

  LD      init/built-in.o
arch/arm/mach-omap2/built-in.o: In function `sr_class3_configure':
arch/arm/mach-omap2/smartreflex-class3.c:44: undefined reference to `sr_configure_errgen'
arch/arm/mach-omap2/built-in.o: In function `sr_class3_disable':
arch/arm/mach-omap2/smartreflex-class3.c:33: undefined reference to `sr_disable_errgen'
arch/arm/mach-omap2/smartreflex-class3.c:35: undefined reference to `sr_disable'
arch/arm/mach-omap2/built-in.o: In function `sr_class3_enable':
arch/arm/mach-omap2/smartreflex-class3.c:28: undefined reference to `sr_enable'
arch/arm/mach-omap2/built-in.o: In function `sr_class3_init':
arch/arm/mach-omap2/smartreflex-class3.c:59: undefined reference to `sr_register_class'
make: *** [vmlinux] Error 1
Signed-off-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>