spapr: Clean up handling of LPCR power-saving exit bits

spapr: Clean up handling of LPCR power-saving exit bits

To prevent spurious wakeups on cpus that are supposed to be disabled, we
need to clear the LPCR bits which control certain wakeup events.
spapr_cpu_reset() has separate cases here for boot and non-boot (initially
inactive) cpus.  rtas_start_cpu() then turns the LPCR bits on when the
non-boot cpus are activated.

But explicit checks against first_cpu are not how we usually do things:
instead spapr_cpu_reset() generally sets things up for non-boot (inactive)
cpus, then spapr_machine_reset() and/or rtas_start_cpu() override as
necessary.

So, do that instead.  Because the LPCR activation is identical for boot
cpus and non-boot cpus just activated with rtas_start_cpu() we can put the
code common in spapr_cpu_set_entry_state().

Signed-off-by: David Gibson <[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Tested-by: Cédric Le Goater <[email protected]>