[ARM] 4504/1: nommu: Fix the ARMv6 support for MMU-less platforms

With this patch, Kconfig only selects CPU_HAS_ASID for the MMU
case. It also corrects the typo in the v6wbi_tlb_fns definition in
pgtable-nommu.h.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>