ANDROID: drm/dsi: Fix byte order of DCS set/get brightness

The MIPI DCS specification demands that brightness values are sent in
big endian byte order. It also states that one parameter (i.e. one byte)
shall be sent/received for 8 bit wide values, and two parameters shall
be used for values that are between 9 and 16 bits wide.

Bug: 139263611
Bug: 139107810
Change-Id: I24306e21ec6a5ff48ea121d977419a81d5b44152
Signed-off-by: Daniel Mentz <danielmentz@google.com>
Signed-off-by: Wilson Sung <wilsonsung@google.com>
(cherry picked from commit 3c373bfd83fd686390ea60a032ff876242c71d49)
Signed-off-by: Saravana Kannan <saravanak@google.com>