alpha: Fix bootpfile and bootpzfile make targets

Fix the bootpfile and bootpzfile make targets to creat BOOTP images.
Both targets were broken due to some missing defines to re-map ELF
constants. In addition the old code used the generic vsprintf function
of the kernel which we now replace by a simple and much smaller
implementation for the bootloader.

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Matt Turner <mattst88@gmail.com>