pvr: Add PVR_DW_TO_BYTES()

pvr: Add PVR_DW_TO_BYTES()

We use dwords (32 bit) quite a bit around the code base. Previously
we used '* 4', '<< 2', or '* sizeof(uint32_t)' to go from dwords to
bytes. The conversion isn't always clear when other operations
happen in the same line, which can leave one wondering where the
multiplication came from.
PVR_DW_TO_BYTES() should make the code more obvious as well as
making the conversion more consistent.

Signed-off-by: Karmjit Mahil <Karmjit.Mahil@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22658>