arm: dma-mapping: page align size before flush tlb

start and end must be page aligned while calling
flush_tlb_kernel_range else the last page may get
missed while invalidation.

Change-Id: I8fa689ea29ad35f5ae78ddef978f678d7e3355bc
Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>