Specify jnilib partition in Android-<target>.mk

Context
- Android-<target>.mk currently does not contain information about partition for its dependent unembedded jni libraries, but only lists the name of the unembedded jni libraries.
- If an android_app module depends on an unembedded jni library that is located in a different partition, make cannot find the library.

Implementation
- Create a string field partition in jniLib struct.
- Add variable "LOCAL_SOONG_JNI_LIBS_PARTITION_<target>", an array of mappings of the name of the jni library to its partition.

Bug: 154162945
Test: m
Change-Id: I6b8e1272ff59dc70e3dd6ce8c6c8e4686dad76df
diff --git a/cc/linkable.go b/cc/linkable.go
index 2316d86..0522fc6 100644
--- a/cc/linkable.go
+++ b/cc/linkable.go
@@ -253,6 +253,9 @@
 
 	// VndkVersion returns the VNDK version string for this module.
 	VndkVersion() string
+
+	// Partition returns the partition string for this module.
+	Partition() string
 }
 
 var (