minix/driver/storage/ramdisk: Makefile rework
minix/driver/storage/ramdisk: Makefile rework

This is an attempt at simplifying the Makefile, by specifying the home
directory of every utility, instead of trying to guess depending on some
variable.

While this is a bit more verbose, this simplifies the logic. This also makes
it simpler to add / remove programs from the ramdisk.

Change-Id: Id789a6cc6e5a9be11decec0f30c5327f19819aa1

veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi