Added support to capture unsch fw debug logs in debugfs.
To enable set amdgpu_umschfw_log =1 in boot args.

v1 - rename variable to umsch_mm_fwlog (Veera)

Signed-off-by: Saleemkhan Jamadar <saleemkhan.jamadar@amd.com>
Reviewed-by: Veerabadhran Gopalakrishnan <Veerabadhran.Gopalakrishnan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>