ppc/xics: change the icp_ routines API to use an 'ICPState *' argument

ppc/xics: change the icp_ routines API to use an 'ICPState *' argument

The routines :

	void icp_set_cppr(ICPState *icp, uint8_t cppr);
	void icp_set_mfrr(ICPState *icp, uint8_t mfrr);
	void icp_eoi(ICPState *icp, uint32_t xirr);

now use one 'ICPState *icp' argument instead of a 'XICSState *' and a
server arguments. The backlink on XICSState* is used whenever needed.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>