arm: exx32: Add Silabs EFM32JG12B soc files

The Silicon Labs EFM32 Jade Gecko MCU includes:

    * Cortex-M3 core at 40MHz
    * up to 1024KB of flash and 256KB of RAM
    * multiple low power peripherals

This is basically the same as the EFM32 Pearl Gecko, but with an ARM
Cortex-M3 core instead of a Cortex-M4F.

Signed-off-by: Christian Taedcke <christian.taedcke@lemonbeat.com>

soc/arm/silabs_exx32/efm32jg12b/linker.ld

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2018 Christian Taedcke
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @file
+ * @brief Linker command/script file
+ *
+ * This is the linker script for both standard images.
+ */
+
+#include <autoconf.h>
+
+#include <arch/arm/cortex_m/scripts/linker.ld>