Revert "core: eos_config: switch optimization level to -O2 by default"

This reverts commit a99cfa812d6a443efbe1c8575f725fb7977bce76.

libstagefright and libhwcompser fail to build on hawrdware/caf with this
they require -0s by default.

Change-Id: Ib04e6ec1033c2475de61420097bf82bd77d27088