parisc: enhance automatic CONFIG_CROSS_COMPILE detection

The current Makefile will only choose the hppa64 cross compiler when running natively on hppa in a 32bit userspace.
This patch additionally chooses the correct 32/64 bit hppa compiler even when doing real cross compiling to hppa/hppa64 from another architecture.

index 5707f1a..ed9a14c 100644
@@ -32,11 +32,6 @@ ifdef CONFIG_64BIT
 UTS_MACHINE	:= parisc64
 CHECKFLAGS	+= -D__LP64__=1 -m64
 WIDTH		:= 64