fbdev/sa1100fb: use vm_iomap_memory()

Use vm_iomap_memory() instead of [io_]remap_pfn_range().
vm_iomap_memory() gives us much simpler API to map memory to userspace,
and reduces possibilities for bugs.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>