powerpc/Makefile: Remove bits related to the previous use of -mcmodel=large

All supported compilers today (gcc v5.1+ and clang v11+) have support for
-mcmodel=medium. As such, NO_MINIMAL_TOC is no longer being set. Remove
NO_MINIMAL_TOC as well as the fallback to -mminimal-toc.

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Naveen N Rao <naveen@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240110141237.3179199-1-naveen@kernel.org