MIPS32: Pass more arguments in registers.

Specifically, use A0-A3,T0-T1 for non-floats and F8-F19 for floats.

Test: booted MIPS32R2 in QEMU
Test: test-art-target-run-test-optimizing (MIPS32R2) on CI20
Test: test-art-target-gtest (MIPS32R2) on CI20
Test: booted MIPS64 (with 2nd arch MIPS32R6) in QEMU
Test: test-art-target-run-test-optimizing (MIPS32R6) in QEMU
Test: test-art-target-gtest (MIPS32R6) in QEMU
Test: test-art-host-gtest

Change-Id: Ib8b0310a109d9f3d70119c1e605e54b013e60728