cmake: gcc: add support for compiling for the ARM Cortex-M1

Add support for compiling for the ARM Cortex-M1 CPU via GCC.

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>
diff --git a/cmake/gcc-m-cpu.cmake b/cmake/gcc-m-cpu.cmake
index 62a51e1..8d6f10d 100644
--- a/cmake/gcc-m-cpu.cmake
+++ b/cmake/gcc-m-cpu.cmake
@@ -8,6 +8,8 @@
     set(GCC_M_CPU cortex-m0)
   elseif(CONFIG_CPU_CORTEX_M0PLUS)
     set(GCC_M_CPU cortex-m0plus)
+  elseif(CONFIG_CPU_CORTEX_M1)
+    set(GCC_M_CPU cortex-m1)
   elseif(CONFIG_CPU_CORTEX_M3)
     set(GCC_M_CPU cortex-m3)
   elseif(CONFIG_CPU_CORTEX_M4)