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/sched.h b/libc/kernel/uapi/linux/sched.h
index b396348..13a34ce 100644
--- a/libc/kernel/uapi/linux/sched.h
+++ b/libc/kernel/uapi/linux/sched.h
@@ -44,6 +44,7 @@
 #define CLONE_NEWPID 0x20000000
 #define CLONE_NEWNET 0x40000000
 #define CLONE_IO 0x80000000
+#ifndef __ASSEMBLY__
 struct clone_args {
   __aligned_u64 flags;
   __aligned_u64 pidfd;
@@ -54,6 +55,8 @@
   __aligned_u64 stack_size;
   __aligned_u64 tls;
 };
+#endif
+#define CLONE_ARGS_SIZE_VER0 64
 #define SCHED_NORMAL 0
 #define SCHED_FIFO 1
 #define SCHED_RR 2