[PARISC] Update minimum compiler version and CROSS_COMPILE for parisc64

Prefix changed in debian, include "gnu" in the commandline.

Signed-off-by: Carlos O'Donell <carlos@parisc-linux.org>

Ensure the compiler version is new enough (>= 3.3)

Signed-off-by: Randolph Chung <tausq@parisc-linux.org>

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