ARM: Replace platform definition of ISA_DMA_THRESHOLD/MAX_DMA_ADDRESS

The values of ISA_DMA_THRESHOLD and MAX_DMA_ADDRESS are related; one is
the physical/bus address, the other is the virtual address.  Both need
to be kept in step, so rather than having platforms define both, allow
them to define a single macro which sets both of these macros
appropraitely.

Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>