ARM: align the start and end of v7_setup_stack to cache line

The v7_setup_stack is used when D-cache disabled. When CPU is reading
something nearby with D-cache enabled. It is possible to read
v7_setup_stack to cache line. There is a risk that when cache line write
back the data, v7_setup_stack may already been modified by other CPU with
D-cache disabled.
The change make v7_setup_stack align cache line size and use the whole
cache line to prevent corrupting v7_setup_stack.

Change-Id: I13be3c49beafd69d6e86ffd28d5f3ba998aaa8c3
Signed-off-by: Cong Zhang <congzhan@codeaurora.org>