media: amphion: Use kmalloc instead of vmalloc

media: amphion: Use kmalloc instead of vmalloc

Replace vmalloc/vfree with kmalloc/kfree for allocating small
driver structures (vpu_inst, vdec_t, venc_t, vpu_cmd_t, and
frame objects).

vmalloc() is designed for large memory allocations and incurs
unnecessary overhead for small objects due to virtual memory
mapping. kmalloc() is more appropriate as it allocates physically
contiguous memory with lower overhead.

ftrace measurements of vpu_alloc_cmd() show significant improvement:

  Before (vmalloc):  35-72 us   (avg ~45.7 us)
  After (kmalloc):   11-26 us   (avg ~16.8 us)

This reduces allocation time by approximately 63%.

No functional changes are intended.

Signed-off-by: Ming Qian <ming.qian@oss.nxp.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>