a4xx: stencil/depth fixes

RB_DEPTH_PITCH actually takes a stride (pitch * cpp), as on a3xx.  Also
add texture format value for NORM_UINT_8_8 used for z16 restore.
a4xx: fix index_size in draw initiator packet
a4xx: rename RB_FS_OUTPUT.ENABLE_BLEND

Seems to enable readback/blend.. give it a better name.
a3xx: instanced vertices setting
a3xx: aniso levels