ARM: 7928/1: kconfig: select HAVE_EFFICIENT_UNALIGNED_ACCESS for CPUv6+ && MMU

Modern ARM CPUs can perform efficient unaligned memory accesses in
hardware and this feature is relied up on by code such as the dcache
word-at-a-time name hashing.

This patch selects HAVE_EFFICIENT_UNALIGNED_ACCESS for these cores and
reworks the kconfig select logic for DCACHE_WORD_ACCESS to use the new
symbol.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
[steven@steven676.net: backport to 3.0: remove DCACHE_WORD_ACCESS stuff,
not present in 3.0]

Change-Id: I156c40bf90de557c9d136b0312cf872e18becf9c