[rtl] Stop rvfi from reporting load information on stores

[SamuelRiedel]

This PR ensures that the trace does not incorrectly report load data during memory store operations. Currently, the tracer uses the rmask and wmask to print information about loads and stores:

ibex/rtl/ibex_tracer.sv

Lines 136 to 145 in 0a13971

	if ((data_accessed & MEM) != 0) begin
	$fwrite(fh, " PA:0x%08x", rvfi_mem_addr);
	if (rvfi_mem_wmask != 4'b0000) begin
	$fwrite(fh, " store:0x%08x", rvfi_mem_wdata);
	end
	if (rvfi_mem_rmask != 4'b0000) begin
	$fwrite(fh, " load:0x%08x", rvfi_mem_rdata);
	end
	end

While the wmask was already gated in the rvfi, the rmask was always enabled, which led to load data being reported even during a store.

[SamuelRiedel]

This will also work for #2336 @Timmmm

[Timmmm]

Nice, thanks for fixing this!

[rswarbrick]

Makes sense to me (and I like the way it's now more symmetrical with the following line too)