intel/tools: Manually set ARF register file/nr/subnr

intel/tools: Manually set ARF register file/nr/subnr

brw_reg::subnr is in bytes, like the subnr field in the instruction
word, but we disassemble the subregister number in units of the type.
For example g0.3<1>F would have a subnr=12.

These non-terminals produce a brw_reg and feed into other non-terminals
that call brw_reg(), where they are passed the subnr that we set here.
brw_reg()'s subnr parameter is expected to be in terms of the register
type, and it is multiplied by the type size to calculate the subnr in
bytes.

In these non-terminals, we don't know the register type yet, so we
must store the subregister number as it was given to us in the .subnr
field and let the brw_reg() constructor handle the conversion to the
canonical byte-based subnr form when it knows the type.

Before this patch, subregister numbers applied to these registers would
be multiplied with the type size twice.

Reviewed-by: Sagar Ghuge <sagar.ghuge@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5956>