Update to v5.13 kernel headers.

Kernel headers coming from:

Git: https://android.googlesource.com/kernel/common/
Branch: android-mainline
Tag: android-mainline-5.13

Test: Builds, bionic unit tests.
Change-Id: Ia4360ca4a2808206f64187dcb234d73c5752624b
diff --git a/libc/kernel/uapi/linux/kexec.h b/libc/kernel/uapi/linux/kexec.h
index b2dc88f..2e3bd0c 100644
--- a/libc/kernel/uapi/linux/kexec.h
+++ b/libc/kernel/uapi/linux/kexec.h
@@ -39,6 +39,7 @@
 #define KEXEC_ARCH_MIPS_LE (10 << 16)
 #define KEXEC_ARCH_MIPS (8 << 16)
 #define KEXEC_ARCH_AARCH64 (183 << 16)
+#define KEXEC_ARCH_RISCV (243 << 16)
 #define KEXEC_SEGMENT_MAX 16
 struct kexec_segment {
   const void * buf;