The recent bump of MAXDSIZ made 32-bit binary execution on 64-bit powerpc fail.
The data segement was too big.

Add a fix-up function like on ia32 for MAXDSIZ.

While here, bring also the MAXSSIZ closer to amd64 and add an equal fix-up
function for MAXSSIZ.

Reviewed by: jhibbits@
Obtained from: jhibbits@
Differential Revision: https://reviews.freebsd.org/D13753