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/fsverity.h b/libc/kernel/uapi/linux/fsverity.h
new file mode 100644
index 0000000..5013567
--- /dev/null
+++ b/libc/kernel/uapi/linux/fsverity.h
@@ -0,0 +1,43 @@
+/****************************************************************************
+ ****************************************************************************
+ ***
+ ***   This header was automatically generated from a Linux kernel header
+ ***   of the same name, to make information necessary for userspace to
+ ***   call into the kernel available to libc.  It contains only constants,
+ ***   structures, and macros generated from the original header, and thus,
+ ***   contains no copyrightable information.
+ ***
+ ***   To edit the content of this header, modify the corresponding
+ ***   source file (e.g. under external/kernel-headers/original/) then
+ ***   run bionic/libc/kernel/tools/update_all.py
+ ***
+ ***   Any manual change here will be lost the next time this script will
+ ***   be run. You've been warned!
+ ***
+ ****************************************************************************
+ ****************************************************************************/
+#ifndef _UAPI_LINUX_FSVERITY_H
+#define _UAPI_LINUX_FSVERITY_H
+#include <linux/ioctl.h>
+#include <linux/types.h>
+#define FS_VERITY_HASH_ALG_SHA256 1
+#define FS_VERITY_HASH_ALG_SHA512 2
+struct fsverity_enable_arg {
+  __u32 version;
+  __u32 hash_algorithm;
+  __u32 block_size;
+  __u32 salt_size;
+  __u64 salt_ptr;
+  __u32 sig_size;
+  __u32 __reserved1;
+  __u64 sig_ptr;
+  __u64 __reserved2[11];
+};
+struct fsverity_digest {
+  __u16 digest_algorithm;
+  __u16 digest_size;
+  __u8 digest[];
+};
+#define FS_IOC_ENABLE_VERITY _IOW('f', 133, struct fsverity_enable_arg)
+#define FS_IOC_MEASURE_VERITY _IOWR('f', 134, struct fsverity_digest)
+#endif