virtio-gpu: add new capset and blob resource featurefor libhsakmt

[energystoryhhl]

Update virtio-gpu documentation for the libhsakmt context.

We are working on enable ROCm /libhsakmt native context by virtio-gpu, it is uesd for GPU computing.
Need add a new cap set for libhsakmt, libhsakmt is like the role of libdrm in MESA.
Need add a new blob resource type called userptr, used for let driver access the userspace memory directly.
Many work is in progress. OpenCL in ROCm is functional currently, and related upstream working is ongoing.
Cause number 7 already achieved by VirCL, so we choice number 8 as the cap set number.

1. VIRTIO_GPU_CAPSET_HSAKMT is used for ROCm/libhsakmt context create.
2. VIRTIO_GPU_BLOB_FLAG_USE_USERPTR for blob userptr resource create.
3. VIRTIO_GPU_F_RESOURCE_USERPTR for blob userptr feature probe.

Latest patches in
https://lore.kernel.org/all/20250228053650.393646-2-honglei1.huang@amd.com/