ARM: 6941/1: cache: ensure MVA is cacheline aligned in flush_kern_dcache_area

The v6 and v7 implementations of flush_kern_dcache_area do not align
the passed MVA to the size of a cacheline in the data cache. If a
misaligned address is used, only a subset of the requested area will
be flushed. This has been observed to cause failures in SMP boot where
the secondary_data initialised by the primary CPU is not cacheline
aligned, causing the secondary CPUs to read incorrect values for their
pgd and stack pointers.

This patch ensures that the base address is cacheline aligned before
flushing the d-cache.

Cc: <stable@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>