ARC: Introduce is_isa_X() functions

ARC: Introduce is_isa_X() functions

Introduce is_isa_arcv2() and is_isa_arcompact() functions.

These functions only check configuration options and return
compile-time constant so they can be used instead of #ifdef's to
to write cleaner code.

Now we can write:
-------------->8---------------
if (is_isa_arcv2())
	ioc_configure();
-------------->8---------------
instead of:
-------------->8---------------
ifdef CONFIG_ISA_ARCV2
	ioc_configure();
endif
-------------->8---------------

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>