powerpc/32: implement HAVE_CONTEXT_TRACKING_USER support

Context tracking involves tracking user, kernel, guest switches. 32-bit
shares interrupt and syscall entry and exit code (and context tracking
calls) with 64-bit, and KVM can not be selected if CONTEXT_TRACKING_USER
is enabled, so context tracking can be enabled for 32-bit.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230121095805.2823731-3-npiggin@gmail.com