Move bootloader.mk to platforms (#18228)

platforms/arm_atsam/bootloader.mk

@@ -0,0 +1,46 @@
+# Copyright 2017 Jack Humbert
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# If it's possible that multiple bootloaders can be used for one project,
+# you can leave this unset, and the correct size will be selected
+# automatically.
+#
+# Sets the bootloader defined in the keyboard's/keymap's rules.mk
+#
+# Current options for ARM (ATSAM):
+#     md-boot      Atmel SAM-BA (only used by Drop boards)
+#
+# If you need to provide your own implementation, you can set inside `rules.mk`
+# `BOOTLOADER = custom` -- you'll need to provide your own implementations. See
+# the respective file under `platforms/<PLATFORM>/bootloaders/custom.c` to see
+# which functions may be overridden.
+
+ifeq ($(strip $(BOOTLOADER)), custom)
+    OPT_DEFS += -DBOOTLOADER_CUSTOM
+    BOOTLOADER_TYPE = custom
+endif
+
+ifeq ($(strip $(BOOTLOADER)), md-boot)
+    OPT_DEFS += -DBOOTLOADER_MD_BOOT
+    BOOTLOADER_TYPE = md_boot
+endif
+
+ifeq ($(strip $(BOOTLOADER_TYPE)),)
+    ifneq ($(strip $(BOOTLOADER)),)
+        $(call CATASTROPHIC_ERROR,Invalid BOOTLOADER,Invalid bootloader specified. Please set an appropriate bootloader in your rules.mk or info.json.)
+    else
+        $(call CATASTROPHIC_ERROR,Invalid BOOTLOADER,No bootloader specified. Please set an appropriate bootloader in your rules.mk or info.json.)
+    endif
+endif