gallivm: add texture target information for sample opcodes to tgsi info

gallivm: add texture target information for sample opcodes to tgsi info

sample opcodes don't have valid texture target information (and I don't think
this should be changed), however it would be nice if we had that information
ready elsewhere, so stuff that information into the tgsi info when analyzing
a shader.

v2: Ilja Mirkin spotted some bugs wrt not handling msaa resources. So add them
and while there also add them to the tex opcode analysis this was cloned from
as well (plus get rid of some bug not detecting indirect textures there in some
cases too).

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>