target-sparc: replace the last tlb entry when no free entries left

Implement the behavior described in the chapter 13.9.11 of
UltraSPARC T1™ Supplement to the UltraSPARC Architecture 2005:

"If a TLB Data-In replacement is attempted with all TLB
entries locked and valid, the last TLB entry (entry 63) is
replaced."

Signed-off-by: Artyom Tarasenko <atar4qemu@gmail.com>
