Enable optimization only for emulator target.

For PDK build, we first build platform.zip then build mini_emulator_ target
to build final images by invoking "PDK_FUSION_PLATFORM_ZIP=x.zip make".
However, in our internal test, I want to have optimization enabled to speed
up booting.

This patch should not break existing PDK build process but at the same time
speed up internal PDK emulator build.

Change-Id: I3c872d77af25accdb93e914679bcc357bf845ba3
1 file changed