ARM: bcm283x: Fix definition of MBOX_TAG_TEST_PIXEL_ORDER

The MBOX_TAG_TEST_PIXEL_ORDER define is incorrect. According to official
documentation it has a slightly different numbering.

Correct mailbox constants are defined in e.g.
linux raspberry-firmware https://code.woboq.org/linux/linux/include/soc/bcm2835/raspberrypi-firmware.h.html#RPI_FIRMWARE_FRAMEBUFFER_TEST_PIXEL_ORDER

These are obtained from the bcm2835 documentation
e.g. https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface#test-pixel-order



Fix the define to get us back in sync with the spec.

Signed-off-by: Berkus Decker <berkus+github@metta.systems>
[agraf: clarify subject, extend commit message]
Signed-off-by: Alexander Graf <agraf@csgraf.de>
[mb: updating email of agraf]
Signed-off-by: Matthias Brugger <mbrugger@suse.com>