soc/intel/apollolake: Add config option for enabling hotplug

PcieRpHotPlug in apollolake UPD is default enabled. This change adds a
config option to enable hotplug only if explicitly requested by
mainboard. This changes the default behavior on all apollolake boards
to have hotplug disabled.

BUG=b:74633273
BRANCH=reef,coral

Change-Id: I572c054d31aaf5d43a79c4b1773ec9356da48d9d
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/25187
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/apollolake/chip.h

@@ -46,6 +46,9 @@ struct soc_intel_apollolake_config {
 	 */
 	uint8_t pcie_rp_clkreq_pin[MAX_PCIE_PORTS];
 
+	/* Enable/disable hot-plug for root ports (0 = disable, 1 = enable). */
+	uint8_t pcie_rp_hotplug_enable[MAX_PCIE_PORTS];
+
 	/* [14:8] DDR mode Number of dealy elements.Each = 125pSec.
 	 * [6:0] SDR mode Number of dealy elements.Each = 125pSec.
 	 */