powerpc: Drop -me200 addition to build flags

Currently a build with CONFIG_E200=y will fail with:

  Error: invalid switch -me200
  Error: unrecognized option -me200

Upstream binutils has never supported an -me200 option. Presumably it
was supported at some point by either a fork or Freescale internal
binutils.

We can't support code that we can't even build test, so drop the
addition of -me200 to the build flags, so we can at least build with
CONFIG_E200=y.

Reported-by: Németh Márton <nm127@freemail.hu>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Scott Wood <oss@buserror.net>
Link: https://lore.kernel.org/r/20201116120913.165317-1-mpe@ellerman.id.au