aom_dsp_rtcd_defs.pl compares most CONFIG_* keys to "yes"
to see if they're set. The script was checking just

  if (aom_config("CONFIG_EXT_PARTITION_TYPES"))

in some cases. The build system doesn't add disabled
configuration options to libs.mk so this is effectively
the same, however it means that setting the config
key explicitly to 0 or "no" in the config headers
was treated the same as setting it to 1 or "yes",
and aom_dsp_rtcd.h would have opposite expections
from aom_config.h or aom_config.asm.

Treat this key similarly to others for consistency.

Change-Id: I27bd7a5532ba4afc2bb289b43b57a1b1971c0348