arc: move CPU flags selection to the main "config.mk"

As a preparation to ARCv2 port submission we're moving CPU slection
flags to a common location.
Also it will allow us to have more flexible CPU specification, not only
ISA version but CPU family as well checking CONFIG_ARC_CPU_xxx.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
2 files changed