ia64_pal_base instead of scanning the EFI tables. This way
AP startup code can more easily use the function.
o Initialize ia64_pal_base in ia64_init(). When the PAL code
doesn't need explicit mapping or no PAL code has been found,
ia64_pal_base will be 0.
o Remove some unused global variables.
o Also in ia64_init(), allocate only 1 page for struct pcpu
and remove some Alpha leftovers.
o Initialize pc_pcb in cpu_pcpu_init().
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