lib: sbi_ipi: Move initial IPI clear to sbi_ipi_init()

sbi_ipi_init() expects the platform warm init function to clear IPIs
on the local hart, but there is already a generic function to do this.
After this change, none of the existing drivers need a warm init
callback.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

platform/nuclei/ux600/platform.c

@@ -212,7 +212,7 @@ static int ux600_ipi_init(bool cold_boot)
 			return rc;
 	}
 
-	return aclint_mswi_warm_init();
+	return 0;
 }
 
 static int ux600_timer_init(void)