Update to android-mainline kernel headers v5.4.

Update generate_uapi_headers.sh to checkout the android mainline
kernel. Also, add a small modification to look for the kernel directory
in common not linux-stable.

Remove deprecated android headers from android/uapi/linux. Also,
remove f_accessory.h since it's in the android mainline kernel.

Test: Builds and runs on walleye.
Change-Id: Ia371305e19f56e6bcc2db6d5b4d299819f07ffc6
diff --git a/libc/kernel/uapi/linux/virtio_ids.h b/libc/kernel/uapi/linux/virtio_ids.h
index f7e1392..8e6712a 100644
--- a/libc/kernel/uapi/linux/virtio_ids.h
+++ b/libc/kernel/uapi/linux/virtio_ids.h
@@ -33,5 +33,6 @@
 #define VIRTIO_ID_VSOCK 19
 #define VIRTIO_ID_CRYPTO 20
 #define VIRTIO_ID_IOMMU 23
+#define VIRTIO_ID_FS 26
 #define VIRTIO_ID_PMEM 27
 #endif