drm/amdgpu : Increase the mes log buffer size as per new MES FW version

From MES version 0x54, the log entry increased and require the log buffer
size to be increased. The 16k is maximum size agreed

Signed-off-by: shaoyunl <shaoyun.liu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>