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>

lib/utils/ipi/fdt_ipi_plicsw.c

@@ -42,6 +42,6 @@ static const struct fdt_match ipi_plicsw_match[] = {
 struct fdt_ipi fdt_ipi_plicsw = {
 	.match_table = ipi_plicsw_match,
 	.cold_init   = fdt_plicsw_cold_ipi_init,
-	.warm_init   = plicsw_warm_ipi_init,
+	.warm_init   = NULL,
 	.exit	     = NULL,
 };