platform: Drop IPI warm init and exit hooks

Now that the SBI IPI core clears IPIs at warm boot in a generic way,
none of the drivers or platforms use these hooks, and we can remove
them. Platforms need only to initialize the driver once during cold
init. If other hooks are needed in the future, they can be added to
struct sbi_ipi_device.

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 +42,4 @@ 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   = NULL,
-	.exit	     = NULL,
 };