powerpc: remove old GCC version checks

powerpc: remove old GCC version checks

BugLink: https://bugs.launchpad.net/bugs/1837477
commit f2910f0e6835339e6ce82cef22fa15718b7e3bfa upstream.

GCC 4.6 is the minimum supported now.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[nc: Applied to minimize unnecessary conflicts]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>