ARM: make virt_to_idmap() return unsigned long

Make virt_to_idmap() return an unsigned long rather than phys_addr_t.

Returning phys_addr_t here makes no sense, because the definition of
virt_to_idmap() is that it shall return a physical address which maps
identically with the virtual address.  Since virtual addresses are
limited to 32-bit, identity mapped physical addresses are as well.

Almost all users already had an implicit narrowing cast to unsigned long
so let's make this official and part of this interface.

Tested-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/reboot.c

@@ -50,7 +50,7 @@ static void __soft_restart(void *addr)
 	flush_cache_all();
 
 	/* Switch to the identity mapping. */
-	phys_reset = (phys_reset_t)(unsigned long)virt_to_idmap(cpu_reset);
+	phys_reset = (phys_reset_t)virt_to_idmap(cpu_reset);
 	phys_reset((unsigned long)addr);
 
 	/* Should never get here. */