ARM: OMAP2+: do not allow SmartReflex to be built as a module

Disable the module option for POWER_AVS since this is currently not
supported.

This patch fixes these error in the case POWER_AVS is set to 'm':

arch/arm/mach-omap2/built-in.o: In function `sr_class3_configure':
arch/arm/mach-omap2/smartreflex-class3.c:43: 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'

Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>
[tony@atomide.com: updated to use relative paths for the build error]
Signed-off-by: Tony Lindgren <tony@atomide.com>