ppc/hash64: Add proper real mode translation support

This adds proper support for translating real mode addresses based
on the combination of HV and LPCR bits. This handles HRMOR offset
for hypervisor real mode, and both RMA and VRMA modes for guest
real mode. PAPR mode adjusts the offsets appropriately to match the
RMA used in TCG, but we need to limit to the max supported by the
implementation (16G).

This includes some fixes by Cédric Le Goater <clg@kaod.org>

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[dwg: Adjusted for differences in my version of the prereq patches]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
