drm/etnaviv: Record GPU visible size of GEM BO separately

drm/etnaviv: Record GPU visible size of GEM BO separately

The GPU visible size of a GEM BO is not necessarily PAGE_SIZE aligned,
which happens when CPU page size is not equal to GPU page size. Extra
precious resources such as GPU page tables and GPU TLBs may being paid
because of this but never get used.

Track the size of GPU visible part of GEM BO separately, ensure no
GPUVA range wasting by aligning that size to GPU page size.

Signed-off-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>