cirrus: cs89x0: remove two obsolete Kconfig macros

The CONFIG_ARCH_IXDP2X01 and CONFIG_MACH_IXDP2351 Kconfig macros are
unused since the ixp23xx and ixp2000 platforms were removed in v3.5. So
remove the last code still depending on these macros. And since
CS89x0_NONISA_IRQ was only set if either of these two macros was defined
we can also remove that macro and the code depending on it.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>