fbdev: kyro: Use devm_ioremap() for mmio registers

Replace the manual ioremap() call for the MMIO registers with the
device-managed devm_ioremap() variant.

This simplifies the driver's resource management by ensuring the memory is
automatically unmapped when the driver detaches from the device.

Signed-off-by: Giovanni Di Santi <giovanni.disanti.lkl@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>