powerpc/powernv/idle: Restore LPCR on wakeup from deep-stop

On wakeup from a deep stop state which is supposed to lose the
hypervisor state, we don't restore the LPCR to the old value but set
it to a "sane" value via cur_cpu_spec->cpu_restore().

The problem is that the "sane" value doesn't include UPRT and the HR
bits which are required to run correctly in Radix mode.

Fix this on POWER9 onwards by restoring the LPCR value whatever it was
before executing the stop instruction.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>