pl050: move logic from pl050_realize() to pl050_init()

pl050: move logic from pl050_realize() to pl050_init()

The logic for initialising the register memory region and the sysbus output IRQ
does not depend upon any device properties and so can be moved from
pl050_realize() to pl050_init().

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: Helge Deller <deller@gmx.de>
Acked-by: Helge Deller <deller@gmx.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20220712215251.7944-7-mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>