dri/i965: fix incorrect rgbFormat in intelCreateBuffer().

dri/i965: fix incorrect rgbFormat in intelCreateBuffer().

It is incorrect to assume that pixel format is always in BGR byte order.
We need to check bitmask parameters (such as |redMask|) to determine whether
the RGB or BGR byte order is requested.

v2: reformat code to stay within 80 character per line limit.
v3: just fix the byte order problem first and investigate SRGB later.
v4: rebased on top of the GLES3 sRGB workaround fix.
v5: rebased on top of the GLES3 sRGB workaround fix v2.

Signed-off-by: Haixia Shi <hshi@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>