cris: No need to append -O2 and $(LINUXINCLUDE)

The make variables asflags-y and ccflags-y are appended with -O2 and
$(LINUXINCLUDE). But the build already picks up -O2 from the top Makefile
and $(LINUXINCLUDE) from scripts/Makefile.lib. The net effect is that -O2
and the (long) list of include directories are used twice.

This is harmless but pointless. So stop appending to these flags.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jesper Nilsson <jespern@axis.com>