ppc: Create cpu_ppc_set_papr() helper

ppc: Create cpu_ppc_set_papr() helper

And move the code adjusting the MSR mask and calling kvmppc_set_papr()
to it. This allows us to add a few more things such as disabling setting
of MSR:HV and appropriate LPCR bits which will be used when fixing
the exception model.

Signed-off-by: Benjamin Herrenschmidt <[email protected]>
Reviewed-by: David Gibson <[email protected]>
[clg: removed LPCR setting ]
Signed-off-by: Cédric Le Goater <[email protected]>
Signed-off-by: David Gibson <[email protected]>