[PARISC] Use F_EXTEND() for COMMAND_GLOBAL

Instead of wrapping the define of COMMAND_GLOBAL in #ifdef __LP64__
use the F_EXTEND() macro defined in asm/io.h, which is the preferred
way of extending mmio space addresses for either 32 or 64 bit machines.

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