Convert CONFIG_SPL_USB_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/am43xx_evm_usbhost_boot_defconfig b/configs/am43xx_evm_usbhost_boot_defconfig
index 1809776..5bc4ef8 100644
--- a/configs/am43xx_evm_usbhost_boot_defconfig
+++ b/configs/am43xx_evm_usbhost_boot_defconfig
@@ -12,6 +12,7 @@
 CONFIG_SPL_STACK_R=y
 CONFIG_SPL_MTD_SUPPORT=y
 CONFIG_SPL_USB_HOST_SUPPORT=y
+CONFIG_SPL_USB_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set
diff --git a/include/configs/am43xx_evm.h b/include/configs/am43xx_evm.h
index d7a96b9..c2fc2c2 100644
--- a/include/configs/am43xx_evm.h
+++ b/include/configs/am43xx_evm.h
@@ -86,9 +86,6 @@
 #define CONFIG_SPL_LDSCRIPT		"$(CPUDIR)/omap-common/u-boot-spl.lds"
 
 /* SPL USB Support */
-#ifdef CONFIG_SPL_USB_HOST_SUPPORT
-#define CONFIG_SPL_USB_SUPPORT
-#endif
 
 #if defined(CONFIG_SPL_USB_HOST_SUPPORT) || !defined(CONFIG_SPL_BUILD)
 #define CONFIG_SYS_USB_FAT_BOOT_PARTITION		1