[MIPSR6] Add mips64r6 and mips32r6 targets

Add mips64r6 target and corresponding mips32r6 target.
Defaults remain as mips64r2 and mips32r2.

Apply -FP64A codegen subsetting to mips32r6 only.
Access FR=0 odd-numbered 32-bit float regs only via
double-prec even-numbered regs, not by single-prec ops.

(cherry picked from commit 6bab974cdc)

Change-Id: I447337ce56c15e86cec505d68a6b45294fc3ba77

core/combo/arch/mips/mips32r6.mk

@@ -0,0 +1,12 @@
+# Configuration for Android on MIPS.
+# Generating binaries for MIPS32R6/hard-float/little-endian
+
+ARCH_MIPS_REV6 := true
+arch_variant_cflags := \
+    -mips32r6 \
+    -mfp64 \
+    -mno-odd-spreg \
+    -msynci
+
+arch_variant_ldflags := \
+    -Wl,-melf32ltsmip

core/combo/arch/mips64/mips64r6.mk

@@ -0,0 +1,7 @@
+# Configuration for Android on mips64r6.
+
+ARCH_MIPS_REV6 := true
+arch_variant_cflags := \
+    -mips64r6 \
+    -msynci
+