ENGR00172374-4: remove platform _adjust_dma_zone function

ENGR00172374-4: remove platform _adjust_dma_zone function

fix the compiling warnings when upgrade to v3.0

arch/arm/mm/init.c:215: warning: 'arm_adjust_dma_zone' defined but not used

The commit: be20902 ARM: use ARM_DMA_ZONE_SIZE to adjust the zone sizes by
Russell has make the _adjust_dma_zone function the common help function, thus
we can remove platform _adjust_dma_zone function by just define:ARM_DMA_ZONE_SIZE

commit be20902ba67de70b38c995903321f4152dee57b7
Author: Russell King <rmk+kernel@arm.linux.org.uk>
Date:   Wed May 11 15:39:00 2011 +0100

    ARM: use ARM_DMA_ZONE_SIZE to adjust the zone sizes

    Rather than each platform providing its own function to adjust the
    zone sizes, use the new ARM_DMA_ZONE_SIZE definition to perform this
    adjustment.  This ensures that the actual DMA zone size and the
    ISA_DMA_THRESHOLD/MAX_DMA_ADDRESS definitions are consistent with
    each other, and moves this complexity out of the platform code.

    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>
Signed-off-by: Jason Liu <r64343@freescale.com>