drm/radeon: fix backend map setup on 1 RB trinity boards
drm/radeon: fix backend map setup on 1 RB trinity boards

Need to adjust the backend map depending on which RB is
enabled.  This is the trinity equivalent of:
f7eb97300832f4fe5fe916c5d84cd2e25169330e

May fix:
https://bugs.freedesktop.org/show_bug.cgi?id=57919

Signed-off-by: Alex Deucher <08dc22c6156113f2deff178e35e3ed9b24d6af9e@amd.com>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs