minigbm: cros_gralloc: Use standard error codes

minigbm: cros_gralloc: Use standard error codes

Since we decided not to support gralloc1 and gralloc0 requires standard
errno-based error codes to be returned to callers, remove the custom
error code enumeration and use standard codes everywhere in
cros_gralloc.

BUG=b:63915090
TEST=Play store starts on Eve

Change-Id: I4f466e8cac6323554f29a7da5c2c00ab47b0abf2
Reviewed-on: https://chromium-review.googlesource.com/580735
Commit-Ready: Tomasz Figa <tfiga@chromium.org>
Tested-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>