nir/inline_uniforms: support loop

nir/inline_uniforms: support loop

Be able to inline uniforms in loop for unrolling it.
Nested loop/if is also supported.

Some example:

    for (i = 0; i < count; i++)
	...

uniform "count" will be inlined. But note this does not
make sure the loop will be unrolled (ie. count = 1000).

    for (i = 0; i < count; i++)
        for (j = init; j < 10; j++)
            if (type == 2)
                ...

uniform "count", "init" and "type" will be inlined.

It is intentional to not be too aggressive to add uniforms
to avoid false positive case while be able to support most
common usage.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11950>