[IA64] fix up bte.h

bte.h expects a #define of L1_CACHE_MASK which is currently only
in bte.c.  This small patch gets bte.h to include cleanly and makes
BTE_UNALIGNED_COPY not report errors.

Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>