powerpc/xive: Untangle xive from child interrupt controller drivers

xive-specific data is stored in handler_data. This creates a mess, as xive
has to rely on child interrupt controller drivers to clean up this data, as
was done by 9a014f45 ("powerpc/pseries/pci: Add a msi_free() handler to
clear XIVE data").

Instead, store xive-specific data in chip_data and untangle the child
drivers.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/83968073022a4cc211dcbd0faccd20ec05e58c3e.1754903590.git.namcao@linutronix.de