sysreset: qemu virt: Use map_sysmem()

sysreset: qemu virt: Use map_sysmem()

In the platform data there is a phys_addr_t (an integer) for the address
of the register and we pass that as-is into writel() which is fine in most
places because we don't need to do any mapping and the macro for writel()
does a cast to a pointer.

If writel() is a static inline function the address argument is a pointer
so passing it in as an integer without casting it first causes warnings or
build failure.

map_sysmem() handles the casting part and if phys_addr_t is 32bits when
on a 64bit machine.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
Acked-by: Kuan-Wei Chiu <visitorckw@gmail.com>