powerpc: remove checks for binutils older than 2.25

Commit e4412739

 ("Documentation: raise minimum supported version of
binutils to 2.25") allows us to remove the checks for old binutils.

There is no more user for ld-ifversion. Remove it as well.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230119082250.151485-1-masahiroy@kernel.org