xen: arm: log warning for interrupt configuration mismatch

xen: arm: log warning for interrupt configuration mismatch

The ICFGR register is not necessarily writeable, in particular it is
IMPLEMENTATION DEFINED for a PPI if the configuration register is
writeable. Log a warning if the hardware has ignored our write and
update the actual type in the irq descriptor so subsequent code can do
the right thing.

This most likely implies a buggy firmware description (e.g.
device-tree).

The issue is observed for example on the APM Mustang board where the
device tree (as shipped by Linux) describes all 3 timer interrupts as
rising edge but the PPI is hard-coded to level triggered (as makes
sense for an arch timer interrupt).

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Julien Grall <julien.grall@linaro.org>
Cc: Pranavkumar Sawargaonkar <psawargaonkar@apm.com>