xen/arm: gic: Introduce GIC_PRI_{IRQ/IPI}_ALL

xen/arm: gic: Introduce GIC_PRI_{IRQ/IPI}_ALL

Introduce macros GIC_PRI_IRQ_ALL and GIC_PRI_IPI_ALL to be used in all
the places where we want to set default priority for all the offsets
in interrupt priority register. This will improve readability and
allow to get rid of introducing variables just to store this value.

Take the opportunity to mark GIC_PRI_{IRQ/IPI} as unsigned values
to suppress static analyzer warnings as they are used in expressions
exceeding integer range (shifting into signed bit). Modify also other
priority related macros to be coherent.

Signed-off-by: Michal Orzel <michal.orzel@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>