powerpc: Remove unused FW_FEATURE_NATIVE references

FW_FEATURE_NATIVE_ALWAYS and FW_FEATURE_NATIVE_POSSIBLE are always
zero and never do anything. Remove them.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211201144153.2456614-2-npiggin@gmail.com