ARM: zynq: Actually remove hotplug.c

Commit 'ARM: zynq: Remove hotplug.c'
(caf86a73) was supposed to remove
hotplug.c - but it didn't. It moved all content from
hotplug.c elsewhere and removed its entry from the Makefile, but missed
to actually remove the whole file. Remove it now.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>