armv7: Move L2CTLR read/write to common

L2CTLR read/write functions are common to armv7 so, move
them in to include/asm/armv7.h and use them where ever it need.

Cc: Tom Warren <twarren@nvidia.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
[Backed out the change to arch/arm/mach-tegra/cache.c:]
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>