Buserr scoreboard bug fixes

Created by: silabs-mateilga

Changes made to make buserr regression pass:

• Changed the rvfi instruction monitor to use mcause rdata in stead of "get_csr_retirement_data()" when determining interrupt cause.
• Allowed buserr_sb to discount buserror instruction matches during debug, as we are not able to observe entries in to exception handler while in debug. This will be changed when RVFI extends intr signal to include cause.
• Temporarily disabled a_dmode_dret_pc_int to remove regression noise until RVFI accounts for kill signals.