systemc: Fix tlm phase ordering in Gem5ToTlmBridge
systemc: Fix tlm phase ordering in Gem5ToTlmBridge

Previously we only rely on timestamp to schedule all phase change events
of tlm transactions in Gem5ToTlmBridge. However, it is valid to have
END_REQ and BEGIN_RESP of a transaction to be scheduled at the same
timestamp and the gem5 scheduler will not necessary order them in a
correct way.

This unfortunately breaks the code as sending a response before
accepting a request doesn't make sense at all and will trigger an
assertion failure.

In this CL we slightly increase the priority of END_REQ event so we can
always process phase change events in a correct order.

Change-Id: Ic33a92162c8c53af3887c7b04090115a38f96866
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/44305
Reviewed-by: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5