This renames a few RV32 configs to follow the convention that names w/o
numbers are for RV32, so that to be in line with majority RV32 configs.
As a result, we have: `nsh` vs `nsh64`, `knsh` vs `knsh64`, `pnsh`
vs `pnsh64`,`flats` vs `flats64`, `nsbi` vs `nsbi64`, `libcxx` vs
`libcxx64` etc. This helps us pick the right config name w/o checking
file contents.
Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>
