config: Change parsing of Addr so hex values work from scripts

config: Change parsing of Addr so hex values work from scripts

When passed from a configuration script with a hexadecimal value (like
"0x80000000"), gem5 would error out. This is because it would call
"toMemorySize" which requires the argument to end with a size specifier (like
1MB, etc).

This modification makes it so raw hex values can be passed through Addr
parameters from the configuration scripts.