gnt should not depends on req on OBI to reg if

[davideschiavone]

https://github.com/pulp-platform/register_interface/blob/master/src/periph_to_reg.sv#L72

as written here, the gnt_o depends on the req

[cousteaulecommandant]

Note that currently rvalid <= gnt_o (meaning that OBI rvalid is only issued when both req (= reg valid) and reg ready are high, i.e., when the reg handshake is complete):

register_interface/src/periph_to_reg.sv

Line 48 in 8e8c209

r_valid_d = gnt_o;

so if @davideschiavone's proposed change is implemented (which I think it should), this line needs to be modified as well to preserve its current functionality rather than using gnt_o directly.

[phsauter]

This is technically legal with the combinational grant option under OBI R-23 which states: gnt (and gntpar) is allowed to combinatorially depend on OBI link inputs.

However, I do agree we should switch to COMB_GNT == False under R-22.