pl031: Update last RTCLR value on write in case it's read back

pl031: Update last RTCLR value on write in case it's read back

The PL031 allows you to read RTCLR, which is meant to give you the last
value written. PL031State has an lr field which is used when reading
from RTCLR, and is present in the VM migration state, but we never
actually update it, so it always reads as its initial 0 value.

Cc: qemu-stable@nongnu.org
Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20240222000341.1562443-1-jrtc27@jrtc27.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>