powerpc/pseries: Get entry and uaccess flush required bits from H_GET_CPU_CHARACTERISTICS

commit 65c7d070

 upstream.

This allows the hypervisor / firmware to describe these workarounds to
the guest.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210503130243.891868-2-npiggin@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>