Add basic little endian support for ppc64le.

Currently kvmtool works well/was designed for big endian ppc64 systems.
This patch adds support for little endian systems

The system does not yet boot as support for h_set_mode is required to help
with exceptions in big endian mode -- first page fault. The support comes in
the next patch of the series

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Will Deacon <will.deacon@arm.com>