broadcom: don't define internal BPP values twice

broadcom: don't define internal BPP values twice

We have a "maximum bpp of all render targets" field for several
packets. For them we were defining manually the possible values. But
all the possible values are the ones defined at the already defined
type "Internal BPP". So in practice we were defining the possible BPP
values twice.

Also for those fields, sometimes we were using the "Internal BPP" type
and in some other cases we were not, so this commit also adds some
consistency.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11976>