Add the mips_dsp_rev build variable.

build/config/mips.gni

Index: build/config/mips.gni
diff --git a/build/config/mips.gni b/build/config/mips.gni
index 512552db1a98e865d700123752020c6d5a63b204..1b406572c73a27227c00addc7d9c02885a5cd234 100644
--- a/build/config/mips.gni
+++ b/build/config/mips.gni
@@ -2,12 +2,35 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# MIPS arch variant.
 if (current_cpu == "mipsel") {
   declare_args() {
+    # MIPS arch variant. Possible values are:
+    #   "r1"
+    #   "r2"
+    #   "r6"
     mips_arch_variant = "r1"
+
+    # MIPS DSP ASE revision. Possible values are:
+    #   0: unavailable
+    #   1: revision 1
+    #   2: revision 2
+    mips_dsp_rev = 0
+
+    # MIPS floating-point ABI. Possible values are:
+    #   "hard": sets the GCC -mhard-float option.
+    #   "soft": sets the GCC -msoft-float option.
+    mips_float_abi = "hard"
+
+    # MIPS32 floating-point register width. Possible values are:
+    #   "fp32": sets the GCC -mfp32 option.
+    #   "fp64": sets the GCC -mfp64 option.
+    #   "fpxx": sets the GCC -mfpxx option.
+    mips_fpu_mode = "fp32"
   }
 } else if (current_cpu == "mips64el") {
+  # MIPS arch variant. Possible values are:
+  #   "r2"
+  #   "r6"
   if (is_android) {
     declare_args() {
       mips_arch_variant = "r6"