lima: introduce a struct describing texture descriptor

lima: introduce a struct describing texture descriptor

Use a struct with bitfields to construct texture descriptor
instead of poking bits in array of uint32_t. It improves code
readability and makes it easier to experiment with unknown fields.

Also fix mipmapping while we're at it - Utgard can have up to 13
levels, but 64 bytes is enough only for 10. Calculate descriptor
size dynamically to account extra levels if we need them.

Reviewed-by: Qiang Yu <yuq825@gmail.com>
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>