drm/amdgpu: add sysfs for Peak Tops Limiter (PTL)

Add per-GPU sysfs files under /sys/class/drm/cardX/device/ptl to
control the Peak Tops Limiter (PTL) feature. Exposes ptl_enable
(enable/disable PTL), ptl_format (set/query preferred formats),
and ptl_supported_formats (list supported formats)

Example usage
-------------
Query PTL status:
    `cat /sys/class/drm/card1/device/ptl/ptl_enable`

Enable PTL:
    `sudo bash -c "echo 1 > /sys/class/drm/card1/device/ptl/ptl_enable"`

Disable PTL:
    `sudo bash -c "echo 0 > /sys/class/drm/card1/device/ptl/ptl_enable"`

Set PTL preferred formats:
    `sudo bash -c "echo I8,F32 > /sys/class/drm/card1/device/ptl/ptl_format"`

Query supported formats:
    `cat /sys/class/drm/card1/device/ptl/ptl_supported_formats`

v3 changes:
 * move N/A to previous format in format show(Alex)
 * fix format check for format store(Alex)
 * drop the ptl declarations into amdgpu_ptl.h(Alex)

v2 changes:
 * add usage commands in commit info (Alex)
 * move amdgpu_ptl_fmt into kgd_kfd_interface.h (Alex)

Signed-off-by: Perry Yuan <perry.yuan@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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