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/lx2160aqds_tfa_SECURE_BOOT_defconfig b/configs/lx2160aqds_tfa_SECURE_BOOT_defconfig
index abb095d..317347b 100644
--- a/configs/lx2160aqds_tfa_SECURE_BOOT_defconfig
+++ b/configs/lx2160aqds_tfa_SECURE_BOOT_defconfig
@@ -105,6 +105,7 @@
 CONFIG_USB=y
 CONFIG_USB_XHCI_HCD=y
 CONFIG_USB_XHCI_DWC3=y
+CONFIG_USB_MAX_CONTROLLER_COUNT=2
 CONFIG_RSA=y
 CONFIG_SPL_RSA=y
 CONFIG_RSA_SOFTWARE_EXP=y