cfi flash support for arm

[Mori Hiroki <yamori813%yahoo.co.jp@localhost>]

Hi

I make code for cfi support for arm.

https://github.com/yamori813/netbsd-src/blob/trunk/sys/arch/arm/mainbus/mainbus_cfi.c

I check armv4,5,6. Do you like this ?

Hiroki Mori