powerpc: Free up CPU feature bits on 64-bit machines

This moves all the CPU feature bits that are only used on 32-bit
machines to the top 20 bits of the CPU feature word and arranges
for them to be defined only in 32-bit builds.  The features that
are common to 32-bit and 64-bit machines are moved to bits 0-11
of the CPU feature word.  This means that for 64-bit platforms,
bits 44-63 can now be used for new features that only exist on
64-bit machines.  (These bit numbers are counting from the right,
i.e. the LSB is bit 0.)

Because CPU_FTR_L3_DISABLE_NAP moved from the low 16 bits to the high
16 bits, we have to adjust some assembly code.  Also, CPU_FTR_EMB_HV
moved from the high 16 bits to the low 16 bits.

Note that CPU_FTR_REAL_LE only applies to 64-bit chips, because only
64-bit chips (POWER6, 7, 8, 9) have a true little-endian mode that is
a CPU execution mode as opposed to being a page attribute.

With this we now have 20 free CPU feature bits on 64-bit machines.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>