arm: correct vfp save/restore asm constraints

arm: correct vfp save/restore asm constraints

Some versions of gcc complain:
> vfp.c: In function 'vfp_restore_state':
> vfp.c:45:27: error: memory input 0 is not directly addressable
> vfp.c:51:31: error: memory input 0 is not directly addressable

There is no way to express the constraint we want (which is the address of the
array, clobbering the whole array). Therefore we have to fake it up by using
two constraints.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Will.Deacon@arm.com
Acked-by: Julien Grall <julien.grall@linaro.org>