Add drivers/ide/arm/ide_arm.c for simple default IDE interfaces
and clean obsolete ide_init_default_hwifs() implementations
in asm-arm/arch-{cl7500,rpc,shark}/ide.h and asm-arm26/ide.h.

This allows us to kill ide_init_default_hwifs() completely
in the next patch (because lh7a40x and sa1100 are broken).

Cross-compile tested on ARM.