Add HAL_PIXEL_FORMAT_BLOB format in cros gralloc

Add HAL_PIXEL_FORMAT_BLOB format in cros gralloc

We convert HAL_PIXEL_FORMAT_BLOB to DRM_FORMAT_R8 for camera picture
taking. Choose DRM_FORMAT_R8 because <system/graphics.h> requires the
buffers with a format HAL_PIXEL_FORMAT_BLOB have a height of 1, and
width equal to their size in bytes.

BUG=b:37692495
TEST=open camera app and take a picture.

Change-Id: I11a82b057b7c1174dd946e0b7d3cbde9c1d630d9
Reviewed-on: https://chromium-review.googlesource.com/487552
Commit-Ready: Heng-ruey Hsu <henryhsu@google.com>
Tested-by: Heng-ruey Hsu <henryhsu@google.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>