Fix the following sparse warning:

drivers/firmware/xilinx/zynqmp.c:32:1: warning: symbol 'pm_api_features_map' was not declared. Should it be static?
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Link: https://lore.kernel.org/r/1606823513-121578-1-git-send-email-zou_wei@huawei.comSigned-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>