ARC: [kbuild] Retire CONFIG_ARC_CPU_REL_4_10

Back when ARC700 4.10 was released, the related kernel features were
tied to this config item so they could be disabled in one shot (i.e.
LLOCK/SCOND, SWAPE, RTSC..)

That having happened a while back, all new ARC customers weill get 4.11+
so those features can be assumed to be present and need not be tied to a
top-level (we still retain the ability to individually disable them).

Further, since ARCv2 also shares some of those feautes, removing it
simplifies things a bit in Kconfig

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>