tu: Align GMEM resolve blit scissor

tu: Align GMEM resolve blit scissor

Even though we normally use the CP_BLIT path with resolves that aren't
aligned, there's a special case when we're resolving the entire image
and there's enough padding so that we can still use CP_EVENT_WRITE::BLIT
when the render area isn't aligned. The hardware seems to not like
unaligned scissors when not clearing, and sometimes hangs rather than
silently round the scissor. This causes hangs in e.g.
dEQP-VK.glsl.derivate.dfdx.texture.msaa4.float_highp.

There was some concern that the CP_BLIT path might use this scissor
also, but I confirmed that this isn't the case by setting it to 0 before
resolving and then noting that CP_BLIT still works (but CP_EVENT_WRITE
doesn't). Furthermore, this is actually impossible because of how the 2D
engine is set up: it gets its own pair of register banks, which can be
switched independently of the 3D register banks, so that 2D events
(CP_BLIT) normally aren't synchronized relative to 3D events
(CP_EVENT_WRITE, CP_DRAW_*, and CP_EXEC_CS) and therefore they can't
share any registers except for non-pipelined registers like RB_CCU_CNTL
that don't use the register bank mechanism at all.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4585>