ARM: cache: remove ARMv3 support code

This is only used by 740t, which is a v4 core and (by my reading of the
datasheet for the CPU) ignores CRm for the cp15 cache flush operation,
making the v4 cache implementation in cache-v4.S sufficient for this
CPU.

Tested with 740T core-tile on Integrator/AP baseboard.

Acked-by: Hyok S. Choi <hyok.choi@samsung.com>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>