powerpc/microwatt: Device-tree updates

Microwatt now implements ISA v3.1 (SFFS compliancy subset), including
prefixed instructions, scv/rfscv, and the FSCR, HFSCR, TAR, and CTRL
registers.  The privileged mode of operation is now hypervisor mode
and there is no privileged non-hypervisor mode; the MSR[HV] bit is
forced to 1.

Besides updating the ibm,powerpc-cpu-features property to reflect the
above, this also makes the following changes relating to peripheral
devices:

- Add gpio controller.
- Remove high-speed property from SD controller, for the case where
  the interface is connected through 200 ohm protection resisters.
- Put an alias for the ethernet in /chosen.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/Z5xtdGSacrWz7swi@thinks.paulus.ozlabs.org