uapi: Add UAPI headers for slatecom_interface driver

Add slatecom_interface header file in gen_headers to make it
accessible from userspace modules who uses Android.bp files
for compilation.

Change-Id: Ie298ec28983c16999d941ee8667e2dd7b5c3db22
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>

gen_headers_arm.bp

@@ -529,6 +529,7 @@ gen_headers_out_arm = [
     "linux/shm.h",
     "linux/signal.h",
     "linux/signalfd.h",
+    "linux/slatecom_interface.h",
     "linux/smc.h",
     "linux/smc_diag.h",
     "linux/smcinvoke.h",