MIPS: Lower LibartImgDeviceBaseAddress() to fix ART tests.

Some of ART tests fail to mmap memory unless
LibartImgDeviceBaseAddress() is further lowered.

Test: booted MIPS32R2 in QEMU
Test: booted MIPS64 (with 2nd arch MIPS32R6) in QEMU
Test: test-art-target-gtest
Test: testrunner.py --target --optimizing
Test: repeat all of the above in configurations
      ART_READ_BARRIER_TYPE=TABLELOOKUP,
      ART_USE_READ_BARRIER=false
Test: repeat the above tests on CI20

Change-Id: I48cd9d8074e07073cc6abb2153660e00017b9e6b

android/config.go

@@ -466,7 +466,7 @@ func (c *config) LibartImgDeviceBaseAddress() string {
 	default:
 		return "0x70000000"
 	case Mips, Mips64:
-		return "0x64000000"
+		return "0x5C000000"
 	}
 }