[$] Support for Intel's Linear Address Masking

A 64-bit pointer can address a lot of memory - far more than just about anyapplication could ever need. As a result, there are bits within that pointer thatare not really needed to address memory, and which might be put to otherneeds. Storing a few bits of metadata within a pointer is a common enoughuse case that multiple architectures are adding support for it at thehardware level. Intel is no exception; support for its "Linear AddressMasking" (LAM) feature has been slowly making its way toward the mainlinekernel.