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..53e441cdb52a1b4d67ef6d821bc55c5c556fb30b 100644
--- a/build/config/mips.gni
+++ b/build/config/mips.gni
@@ -2,7 +2,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# MIPS arch variant.
+# MIPS arch variant. Possible values are:
+# For mipsel:
+#   "r1"
+#   "r2"
+#   "r6"
+# For mips64el:
+#   "r2"
+#   "r6"
 if (current_cpu == "mipsel") {
   declare_args() {
     mips_arch_variant = "r1"
@@ -18,3 +25,24 @@ if (current_cpu == "mipsel") {
     }
   }
 }
+
+if (current_cpu == "mipsel") {
+  declare_args() {
+    # 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"
+    #   "soft"
+    mips_float_abi = "hard"
+
+    # MIPS32 floating-point register width. Possible values are:
+    #   "fp32"
+    #   "fp64"
+    #   "fpxx"
+    mips_fpu_mode = "fp32"
+  }
+}