[OpenBIOS] PATCH: Read the diagnostic mode setting from NVRAM

[Mark Cave-Ayland]

Hi everyone,

When trying to boot a SPARC64 disk image under QEMU, extra diagnostic 
information can be made available on the console if diagnostic-mode? 
returns true. This patch implements the simple step of reading the 
diag-switch? NVRAM parameter and using this to determine whether 
diagnostic mode is enabled or disabled.

ATB,

Mark.