accel/ivpu: Use GEM shmem helper for all buffers

Use struct drm_gem_shmem_object as a base for struct ivpu_bo.
This cuts by 50% the buffer management code.

Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231031073156.1301669-5-stanislaw.gruszka@linux.intel.com