[SPARC64]: Kill out-of-date commentary in asm-sparc64/tsb.h

 * choose to use bit 47 in the tag.  Also, since we never map anything

 * at page zero in context zero, we use zero as an invalid tag entry.

 * When the lock bit is set, this forces a tag comparison failure.

 *

 * Currently, we allocate an 8K TSB per-process and we use it for both

 * I-TLB and D-TLB misses.  Perhaps at some point we'll add code that

 * monitors the number of active pages in the process as we get

 * major/minor faults, and grow the TSB in response.  The only trick

 * in implementing that is synchronizing the freeing of the old TSB

 * wrt.  parallel TSB updates occuring on other processors.  On

 * possible solution is to use RCU for the freeing of the TSB.

 */

#define TSB_TAG_LOCK_BIT	47