platform/x86: Move Mellanox platform hotplug driver to platform/mellanox

In preparation for making the hotplug driver build for different
architectures, move mlxcpld-hotplug.c to platform/mellanox and the
header to include/linux/platform_data as mlxreg.h to reflect the new
interface changes to come.

Replace references to CPLD with REG throughout the files, consistent
with the new name.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
[dvhart: update copyright, rewrite commit message]
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
diff --git a/drivers/platform/mellanox/Makefile b/drivers/platform/mellanox/Makefile
new file mode 100644
index 0000000..7c8385e
--- /dev/null
+++ b/drivers/platform/mellanox/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for linux/drivers/platform/mellanox
+# Mellanox Platform-Specific Drivers
+#
+obj-$(CONFIG_MLXREG_HOTPLUG)	+= mlxreg-hotplug.o