accel/ivpu: Add ivpu_bo_vaddr() and ivpu_bo_size()

Use:
  - ivpu_bo_vaddr(bo) instead of bo->kvaddr
  - ivpu_bo_size(bo) instead of bo->base.size

This is a preparation for switch to a drm_gem_shmem_object as a base for
ivpu_bo, where:
  - bo->kvaddr becomes bo->base.vaddr
  - bo->base.size becomes bo->base.base.size

Using ivpu_bo_vaddr() and ivpu_bo_size() increases the readability of
the code.

Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Reviewed-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901094957.168898-9-stanislaw.gruszka@linux.intel.com