powerpc: Drop -fno-dwarf2-cfi-asm

The original commit/discussion adding -fno-dwarf2-cfi-asm refers to
R_PPC64_REL32 relocations not being handled by our module loader:
http://lkml.kernel.org/r/20090224065112.GA6690@bombadil.infradead.org



However, that is now handled thanks to commit 9f751b82
("powerpc/module: Add support for R_PPC64_REL32 relocations").

So, drop this flag from our Makefile.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9b22a064de6eb1301d92177eb3a38559df7005d3.1583415544.git.naveen.n.rao@linux.vnet.ibm.com