pdc_stable v0.30:

This patch introduces 3 more files to the /sys/firmware/stable tree:
- diagnostic, which contains a cryptic hex string
- osdep1, a 16 bytes os-dependent storage area always available
- osdep2, another os-dependent storage area which existence/size depends
on hversion.

This patch also adds code to setup the "Linux" signature in stable
storage. That is to say that starting with this patch, the kernel will
now sign its OSID (0x0006, thx LaMont) in Stable Storage upon boot,
whether pdc_stable is enabled or not.

Signed-off-by: Thibaut VARENE <varenet@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>