nrf/Makefile: Add bootloader specific section.

Add the option for "mpconfigboard.mk" to define whether the
board hosts a bootloader or not. The BOOTLOADER make variable
must be set to the name of the bootloader.

When the BOOTLOADER name is set it is also required to supply
the BOOTLOADER_VERSION_MAJOR and the BOOTLOADER_VERSION_MINOR
from the "mpconfigboards.mk". These will be used to resolve which
bootloader linker script that should be passed to the linker.

The BOOTLOADER section also supplies the C-compiler with
BOOTLOADER_<bootloader name>=<version major><version minor>
as a compiler define. This is for future use in case a bootloader
needs to do modification to the startup files or similar (like
setting the VTOR specific to a version of a bootloader).

ports/nrf/Makefile

@@ -26,6 +26,13 @@ else
 	include drivers/bluetooth/bluetooth_common.mk
 endif
 
+ifneq ($(BOOTLOADER),)
+	BOOTLOADER_UPPER = $(shell echo $(BOOTLOADER) | tr '[:lower:]' '[:upper:]')
+	# Use additional bootloader linker script
+	LD_FILES += boards/$(MCU_SUB_VARIANT)_$(BOOTLOADER)_$(BOOTLOADER_VERSION_MAJOR).$(BOOTLOADER_VERSION_MINOR).x.ld
+	CFLAGS += -DBOOTLOADER_$(BOOTLOADER_UPPER)_VERSION=$(BOOTLOADER_MAJOR)$(BOOTLOADER_MINOR)
+endif
+
 LD_FILES += boards/memory.ld boards/common.ld
 
 ifneq ($(LD_FILE),)