config: Make parameter conversion handle integers in other bases.

config: Make parameter conversion handle integers in other bases.

Python's float() function/type can't handle hexadecimal notation, but
int() can. Since there are also cases where converting to a float and
then back to an int (or long) can cause rounding error, this change
splits toFloat and toInteger apart and makes them call a worker
function which accepts a conversion function which does the work of
converting a numeric string into an actual number.

in the case of toFloat, it still uses the standard float(), and in the
case of toInteger it uses a lambda which wraps int(x, 0).

Change-Id: Ic46cf4ae86b7eba6f55d731d1b25e3f84b8bb64c
Reviewed-on: https://gem5-review.googlesource.com/c/16504
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>