MIPS: drop incaip board

This is dead hardware and no one is interested in making the
necessary changes for upcoming features like generic board or
driver model.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>

arch/mips/include/asm/u-boot-mips.h

@@ -21,5 +21,3 @@ static inline unsigned long image_copy_end(void)
 	extern char __image_copy_end[];
 	return (unsigned long) &__image_copy_end;
 }
-
-extern int incaip_set_cpuclk(void);