tools/nolibc: MIPS: fix clobbers of 'lo' and 'hi' registers on different ISAs

tools/nolibc: MIPS: fix clobbers of 'lo' and 'hi' registers on different ISAs

All MIPS ISAs before r6 use the 'lo' and 'hi' special registers.
These are clobbered by system calls and need to be marked as such to
avoid miscompilations. Currently nolibc ties the clobbers to the ABI.
But this is wrong and leads to ISA<->ABI combinations which are not
handled correctly, leading to compiler errors or miscompilations.

Handle all different combinations of ABI and ISA.

Fixes: a6a2a8a42972 ("tools/nolibc: MIPS: add support for N64 and N32 ABIs")
Fixes: 66b6f755ad45 ("rcutorture: Import a copy of nolibc")
Suggested-by: Maciej W. Rozycki <macro@orcam.me.uk>
Link: https://lore.kernel.org/lkml/alpine.DEB.2.21.2603141744240.55200@angie.orcam.me.uk/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://patch.msgid.link/20260317-nolibc-mips-clobber-v2-1-5b9a97761a9e@linutronix.de
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>