drm/amdgpu: Fix warnings in gmc_v10_0.c

Fix below checkpatch warnings:

WARNING: Consider removing the code enclosed by this #if 0 and its #endif
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
WARNING: quoted string split across lines

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>