drm/amdgpu: add UMA allocation interfaces to sysfs

drm/amdgpu: add UMA allocation interfaces to sysfs

Add a uma/ directory containing two sysfs files as interfaces to
inspect or change UMA carveout size. These files are:

- uma/carveout_options: a read-only file listing all the available
  UMA allocation options and their index.

- uma/carveout: a file that is both readable and writable. On read,
  it shows the index of the current setting. Writing a valid index
  into this file allows users to change the UMA carveout size to that
  option on the next boot.

Co-developed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Yo-Jung Leo Lin (AMD) <Leo.Lin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>