[PowerPC64LE] powernv ILE setup code.

When running without a hypervisor, we need to set the ILE bit in the LPCR
ourselves.

For the boot processor, handle it in powernv_attach() like we do for other
LPCR bits.

No change for the APs, as they will use the lpcr global to set up their own
LPCR when they do their own cpudep_ap_early_bootstrap() and pick up this
automatically.

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