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/asm-x86/asm/unistd.h b/libc/kernel/uapi/asm-x86/asm/unistd.h
index 8cab383..4bb90cf 100644
--- a/libc/kernel/uapi/asm-x86/asm/unistd.h
+++ b/libc/kernel/uapi/asm-x86/asm/unistd.h
@@ -18,7 +18,7 @@
  ****************************************************************************/
 #ifndef _UAPI_ASM_X86_UNISTD_H
 #define _UAPI_ASM_X86_UNISTD_H
-#define __X32_SYSCALL_BIT 0x40000000
+#define __X32_SYSCALL_BIT 0x40000000UL
 #ifdef __i386__
 #include <asm/unistd_32.h>
 #elif defined(__ILP32__)