hvm/params: add a new delivery type for event-channel in HVM_PARAM_CALLBACK_IRQ

hvm/params: add a new delivery type for event-channel in HVM_PARAM_CALLBACK_IRQ

This new delivery type which is for ARM shares the same value with
HVM_PARAM_CALLBACK_TYPE_VECTOR which is for x86.

val[15:8] is flag: val[7:0] is a PPI.
To the flag, bit 8 stands the interrupt mode is edge(1) or level(0) and
bit 9 stands the interrupt polarity is active low(1) or high(0).

Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Acked-by: Jan Beulich <jbeulich@suse.com>