arm: dma-mapping: set the proper bitmap size

Set the size of bitmap area properly to ensure the proper iova address
to be returned by the bitmap_() API's through alloc_iova(). The current
implementation causes the bitmap index search out of bounds of a page
which can lead to the randomn corruption issues.
This also merge the commit:I66eb15cdbb3 changes.

Change-Id: Ie57ca0b7465c91d318145ed270b7d47d822c8eeb
Fixes:I88ddd98a76b ("arm/arm64: dma-mapping: Fix iova region size")
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>