arm: vexpress: Decouple vexpress-poweroff implementation from machine_desc

This patch adds the pm_power_off and arm_pm_restart variable settings to
the vexpress-poweroff.c driver to decouple it from the machine_desc
definition.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Pawel Moll <pawel.moll@arm.com>

include/linux/vexpress.h

@@ -115,9 +115,6 @@ unsigned __vexpress_get_site(struct device *dev, struct device_node *node);
 void vexpress_sysreg_early_init(void __iomem *base);
 void vexpress_sysreg_of_early_init(void);
 
-void vexpress_power_off(void);
-void vexpress_restart(char str, const char *cmd);
-
 /* Clocks */
 
 struct clk *vexpress_osc_setup(struct device *dev);