broadcom/vc5: Enable UIF XOR on textures.

broadcom/vc5: Enable UIF XOR on textures.

This should increase performance by reducing SDRAM bank conflicts when
crossing between UIF columns (particularly on power-of-two height
textures).

The uif_xor_disable setup is dropped, since we need to allow XOR on lower
miplevels even when level 0 is XOR.  The level 0 force UIF and level 0 XOR
flags should handle setting XOR properly on imported buffers.