Bump linux and riscv-gnu-toolchain

This now contains the latest toolchain release, along with a our Linux
port applied on top of 4.14-rc8.  The toolchain is in good shape: it's
based on stable releases, with every backported patch having landed
upstraem.  Linux hasn't landed upstream yet, so while there's been some
review it will get rebased (and archived).

This builds and boots on both Spike and Freedom.

Makefile

@@ -51,6 +51,7 @@ $(toolchain_dest)/bin/$(target)-gcc: $(toolchain_srcdir)
 	mkdir -p $(toolchain_wrkdir)
 	cd $(toolchain_wrkdir); $(toolchain_srcdir)/configure --prefix=$(toolchain_dest)
 	$(MAKE) -C $(toolchain_wrkdir) linux
+	sed 's/^#define LINUX_VERSION_CODE.*/#define LINUX_VERSION_CODE 263682/' -i $(toolchain_dest)/sysroot/usr/include/linux/version.h
 
 $(buildroot_tar): $(buildroot_srcdir) $(RISCV)/bin/$(target)-gcc
 	$(MAKE) -C $< RISCV=$(RISCV) PATH=$(PATH) O=$(buildroot_wrkdir) riscv64_defconfig

linux

@@ -1 +1 @@
-Subproject commit 2746561a98e127f82876a56609ae9d324a449172
+Subproject commit 160fa8470d0f78b1571c04da8b9af50ac05be378

riscv-gnu-toolchain

@@ -1 +1 @@
-Subproject commit 8b16c6123d3dc9642ceeaa6ad371f494d5970873
+Subproject commit b4dae89f85bf882852c6186b1284df11065bfcd9