gallium: add GS_INVOCATIONS property

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
mesa/st: translate gl_SampleMaskIn to SAMPLEMASK semantic

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
mesa/st: translate gl_InvocationID to INVOCATIONID semantic

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nvc0/ir: add support for SAMPLEMASK sysval

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nvc0/ir: add support for INVOCATIONID system value

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nvc0/ir: set instance count based on the GS_INVOCATIONS property

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nvc0/ir: set gatherComp for non-shadow targets

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nvc0/ir: fetch shadow value from proper place for TG4 cube array

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>