swr: move msaa resolve to generalized StoreTile

swr: move msaa resolve to generalized StoreTile

v3: list piglit tests fixed by this patch. Fixed typo Tim pointed out.
v2: Reword commit message to more closely adhere to community
guidelines.

This patch moves msaa resolve down into core/StoreTiles where the
surface format conversion routines are available.  The previous
"experimental" resolve was limited to 8-bit unsigned render targets.

This fixes a number of piglit msaa tests by adding resolve support for
all the render target formats we support.

Specifically:
layered-rendering/gl-layer-render: fail->pass
layered-rendering/gl-layer-render-storage: fail->pass
multisample-formats *[2,4,8,16] gl_arb_texture_rg: crash->pass
multisample-formats *[2,4,8,16] gl_ext_texture_snorm: crash->pass
multisample-formats *[2,4,8,16] gl_arb_texture_float: fail->pass
multisample-formats *[2,4,8,16] gl_arb_texture_rg-float: fail->pass

MSAA is still disabled by default, but can be enabled with
"export SWR_MSAA_MAX_COUNT=4" (1,2,4,8,16 are options)
The default is 0, which is disabled.

This patch improves the number of multisample-formats supported by swr,
and fixes several crashes currently in the 17.1 branch.  Therefore, it
should be considered for inclusion in the 17.1 stable release.  Being
disabled by default, it poses no risk to most users of swr.

Reviewed-by: Tim Rowley <timothy.o.rowley@intel.com>
cc: mesa-stable@lists.freedesktop.org