Add a sub-HAL implementation for testing multi-HAL

Creates a fake sub-HAL using the default implementation for sensors HAL
2.0 with some small modifications to support the multi-HAL interface.

This sub-HAL can be configured to support two different sets of sensors
making it easier to build and load two different sub-HAL implementations
onto device and verify the multihal implementation works.

Bug: 136511617
Test: compile only. Once multihal can load in sub-HALs, then this can be
accurately tested.

Change-Id: I9b136506bdbc8a3b196fd363748bddfcdd564daf
diff --git a/sensors/2.0/multihal/Android.bp b/sensors/2.0/multihal/Android.bp
index 4dec768..f0b33e4 100644
--- a/sensors/2.0/multihal/Android.bp
+++ b/sensors/2.0/multihal/Android.bp
@@ -23,6 +23,9 @@
         "HalProxy.cpp",
     ],
     init_rc: ["android.hardware.sensors@2.0-service-multihal.rc"],
+    header_libs: [
+        "android.hardware.sensors@2.0-subhal.header",
+    ],
     shared_libs: [
         "android.hardware.sensors@1.0",
         "android.hardware.sensors@2.0",
@@ -36,3 +39,9 @@
     ],
     vintf_fragments: ["android.hardware.sensors@2.0-multihal.xml"],
 }
+
+cc_library_headers {
+    name: "android.hardware.sensors@2.0-subhal.header",
+    vendor: true,
+    export_include_dirs: ["include"],
+}
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