spapr_hcall: Fix little-endian resource handling in H_SET_MODE

This changes resource code definitions to ones used in the host kernel.

This fixes H_SET_MODE_RESOURCE_LE (switch between big endian and
little endian) to sync registers from KVM before changing LPCR value.

This adds a set_spr() helper to update an SPR in a CPU's context to avoid
possible races and makes use of it to change LPCR.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>