remove --gem5, use --emulator gem5 everywhere

Allow passing --emulator multiple times for transparent tests selection
just like --arch.

gem5-bench-cache

@@ -13,7 +13,7 @@ while getopts "C" OPT; do
   esac
 done
 shift "$(($OPTIND - 1))"
-common_opts="--gem5 $@"
+common_opts="--emulator gem5 $@"
 
 # Vars
 cmd="./run ${common_opts}"