drm/amd/display: Clean up style problems in amdgpu_dm_hdcp.c

[ Upstream commit a19de9db ]

Conform to Linux kernel coding style.

And promote sysfs entry for set/get srm to kdoc.

Suggested-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Stable-dep-of: be593d9d ("drm/amd/display: Fix slab-use-after-free in hdcp")
Signed-off-by: Sasha Levin <sashal@kernel.org>