Remove PAE special-case 2GB DMA boundary and always use a 4GB boundary

now that DMA tags in PAE kernels support 4GB boundaries.

Reviewed by:	yongari

sys/dev/bge/if_bgereg.h

@@ -2691,15 +2691,11 @@ struct bge_gib {
 #define	BGE_DMA_MAXADDR		0xFFFFFFFFFF
 #endif
 
-#ifdef PAE
-#define	BGE_DMA_BNDRY		0x80000000
-#else
 #if (BUS_SPACE_MAXADDR > 0xFFFFFFFF)
 #define	BGE_DMA_BNDRY		0x100000000
 #else
 #define	BGE_DMA_BNDRY		0
 #endif
-#endif
 
 /*
  * Ring structures. Most of these reside in host memory and we tell