powerpc/powernv: Fix XSCOM address mangling for form 1 indirect

POWER9 adds form 1 scoms. The form of the indirection is specified in
the top nibble of the scom address.

Currently we do some (ugly) bit mangling so that we can fit a 64 bit
scom address into the debugfs interface. The current code only shifts
the top bit (indirect bit).

This patch changes it to shift the whole top nibble so that the form
of the indirection is also shifted.

This patch is backwards compatible with older scoms.

(This change isn't required in the arch/powerpc/platforms/powernv/opal-prd.c
scom interface as it passes the whole 64bit scom address without any bit
mangling)

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>