[PATCH] powerpc: Change firmware_has_feature() to a macro

So that we can use firmware_has_feature() in a BUG_ON() and have the compiler
elide the code entirely if the feature can never be set, change
firmware_has_feature to a macro. Unfortunate, but necessary at least until
GCC bug #26724 is fixed.

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