nouveau: add support for nir

nouveau: add support for nir

not all those nir options are actually required, it just made the work a
little easier.

v2: fix asserts
    parse compute shaders
    don't lower bitfield_insert
v3: fix memory leak
v4: don't lower fmod32
v5: set lower_all_io_to_temps to false
    fix memory leak because we take over ownership of the nir shader
    merge: use the lowering helper
v6: include TGSI debug header for proper assert call
    add nv50 support
v7: fix Automake build
v8: free shader only for the set shader type
v9: check for IR type inside get_compiler_options
    squash "nouveau: add env var to make nir default"
    fix memory leak when creating compute shaders
    use debug_get_bool_option as it is available in non debug builds
    return failure if unsupported IR is encountered
    don't lower fpow in nir
    lower int 64 divmod inside nir to prevent crashes

Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Pierre Moreau <pierre.morrow@free.fr>