x86: kconfig: Move USB to platform Kconfig

Like other peripheral drivers, move USB related drivers to platform
Kconfig as well.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/broadwell/Kconfig b/arch/x86/cpu/broadwell/Kconfig
index c56f90d..7e71325 100644
--- a/arch/x86/cpu/broadwell/Kconfig
+++ b/arch/x86/cpu/broadwell/Kconfig
@@ -14,6 +14,8 @@
 	imply INTEL_BROADWELL_GPIO
 	imply SCSI
 	imply SPI_FLASH
+	imply USB
+	imply USB_EHCI_HCD
 	imply VIDEO_BROADWELL_IGD
 
 if INTEL_BROADWELL