Add sdk_version to the 'gemmlowp_headers' module

Add the sdk_version to a cc_library_headers module 'gemmlowp_headers', which is
needed in converting .mk files including this module to a .bp file.
Please check the bug below for more details.

Cherrypicked from Ic3abcb6b7e80a96a0a8461f79f8ffe6f86200566

Bug: 217166138
Test: rum 'm module-name'
Test: TreeHugger
Change-Id: Ic3abcb6b7e80a96a0a8461f79f8ffe6f86200566
Merged-In: Ic3abcb6b7e80a96a0a8461f79f8ffe6f86200566
diff --git a/Android.bp b/Android.bp
index 5efb5ff..52becb6 100644
--- a/Android.bp
+++ b/Android.bp
@@ -59,6 +59,7 @@
         "test_com.android.neuralnetworks",
         "//apex_available:platform",
     ],
+    sdk_version: "current",
 }
 
 subdirs = ["eight_bit_int_gemm"]