arm: add mach-nexell (all files except header files)

Changes in relation to FriendlyARM's U-Boot nanopi2-v2016.01:
- SPL not supported yet --> no spl-directory in arch/arm/mach-nexell.
  Appropriate line in Makefile removed.
- clock.c: 'section(".data")' added to declaration of clk_periphs[] and
  core_hz.
- Kconfig: Changes to have a structure like in mach-bcm283x/Kconfig,
  e.g. "config ..." entries moved from other Kconfig.
- timer.c: 'section(".data")' added to declaration of timestamp and
  lastdec.
- arch/arm/mach-nexell/serial.c removed because this is for the UARTs
  of the S5P6818 SoC which is not supported yet. S5P4418 UARTs are
  different, here the (existing) PL011-code is used.
- '#ifdef CONFIG...' changed to 'if (IS_ENABLED(CONFIG...))' where
  possible (and similar).

Signed-off-by: Stefan Bosch <stefan_b@posteo.net>
diff --git a/arch/arm/mach-nexell/Makefile b/arch/arm/mach-nexell/Makefile
new file mode 100644
index 0000000..10b3963
--- /dev/null
+++ b/arch/arm/mach-nexell/Makefile
@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# (C) Copyright 2016 Nexell
+# Hyunseok, Jung <hsjung@nexell.co.kr>
+
+obj-y				+= clock.o
+obj-y				+= timer.o
+obj-y				+= reset.o
+obj-y				+= nx_gpio.o
+obj-y				+= tieoff.o
+obj-$(CONFIG_ARCH_S5P4418)	+= reg-call.o
+obj-$(CONFIG_ARCH_S5P4418)	+= nx_sec_reg.o
+obj-$(CONFIG_CMD_BOOTL)		+= cmd_boot_linux.o