Convert CONFIG_USB_MAX_CONTROLLER_COUNT to Kconfig

This converts the following to Kconfig:
   CONFIG_USB_MAX_CONTROLLER_COUNT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P5040DS_defconfig b/configs/P5040DS_defconfig
index 7e54387..8d5f107 100644
--- a/configs/P5040DS_defconfig
+++ b/configs/P5040DS_defconfig
@@ -87,6 +87,7 @@
 CONFIG_FSL_ESPI=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_FSL=y
+CONFIG_USB_MAX_CONTROLLER_COUNT=2
 CONFIG_USB_STORAGE=y
 CONFIG_ADDR_MAP=y
 CONFIG_SYS_NUM_ADDR_MAP=64