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: NArtyom Tarasenko <atar4qemu@gmail.com>

target/sparc/ldst_helper.c

@@ -246,9 +246,11 @@ static void replace_tlb_1bit_lru(SparcTLBEntry *tlb,
     }
 
 #ifdef DEBUG_MMU
-    DPRINTF_MMU("%s lru replacement failed: no entries available\n", strmmu);
+    DPRINTF_MMU("%s lru replacement: no free entries available, "
+                "replacing the last one\n", strmmu);
 #endif
-    /* error state? */
+    /* corner case: the last entry is replaced anyway */
+    replace_tlb_entry(&tlb[63], tlb_tag, tlb_tte, env1);
 }
 
 #endif