cargo: Add support for building OpenTitan apps

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
diff --git a/.cargo/config b/.cargo/config
index 818ce68..98ba621 100644
--- a/.cargo/config
+++ b/.cargo/config
@@ -13,6 +13,13 @@
   "-D", "warnings",
 ]
 
+[target.riscv32imc-unknown-none-elf]
+rustflags = [
+  "-C", "link-arg=-Topentitan_layout.ld",
+  "-C", "relocation-model=static",
+  "-D", "warnings",
+]
+
 # Target configuration for the travis CI Linux build
 [target.x86_64-unknown-linux-gnu]
 rustflags = [