arm: v7: Kconfig: Rename CPU_V7 as CPU_V7A

Currently CPU_V7 kconfig symbol supports only ARMv7A architectures under
armv7 folder. This led to a misconception of creating separate folders
for armv7m and armv7r. There is no reason to create separate folder for
other armv7 based architectures when it can co-exist with few Kconfig
symbols.

As a first step towards a common folder, rename CPU_V7 as CPUV7A. Later
separate Kconfig symbols can be added for CPU_V7R and CPU_V7M and
can co exist in the same folder.

Reviewed-by: Tom Rini <trini@konsulko.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Suggested-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>