Remove armv6 references from the build system.

We no longer support armv6 and the corresponding
optimized source files have been removed. This
commit removes support for the target and its
media instruction set extensions from the build
system as well.

Once armv6 jobs are removed from the integration
config we can start rejecting --enable/disable-media.

Also reject --enable-edsp.

Change-Id: I547dcc95adb3479d0232396952e72efe2a1343b9