r600/sfn: Set minimum required registers based on array allocation

r600/sfn: Set minimum required registers based on array allocation

In the rare case that after register allocation the highest directly
accessed register index is below the highest value used for an
indirectly accessed array we have to ensure that the shader allocates
enough registers to account for these indices that are not seen by the
assembler.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/7966
Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20451>