broadcom/compiler: allow instruction merges in v71

broadcom/compiler: allow instruction merges in v71

In v3d 4.x there were restrictions based on the number of raddrs used
by the combined instructions, but we don't have these restrictions in
v3d 7.x.

It should be noted that while there are no restrictions on the number
of raddrs addressed, a QPU instruction can only address a single small
immediate, so we should be careful about that when we add support for
small immediates.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25450>