MIPS: java.lang.Integer.valueOf intrinsic.

Test: run-test --64 --optimizing 640-checker-integer-valueof
Test: run-test --64 640-checker-integer-valueof
Test: run-test --64 --no-prebuild --optimizing 640-checker-integer-valueof
Test: run-test --64 --no-prebuild 640-checker-integer-valueof
Test: run-test --optimizing 640-checker-integer-valueof
Test: run-test 640-checker-integer-valueof
Test: run-test --no-prebuild --optimizing 640-checker-integer-valueof
Test: run-test --no-prebuild 640-checker-integer-valueof
Test: mma test-art-host
Test: mma test-art-target

Booted on both MIPS32 and MIPS64 emulators.

Change-Id: I5b2f21cf2334c392080cff9654150504207f4c01