Convert CONFIG_CMD_FPGA_LOADBP et al to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_FPGA_LOADBP
   CONFIG_CMD_FPGA_LOADFS
   CONFIG_CMD_FPGA_LOADMK
   CONFIG_CMD_FPGA_LOADP

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/Kconfig b/arch/Kconfig
index 2528f50..77e1a3e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -86,6 +86,7 @@
 	select DM_SPI_FLASH
 	select USB_EHCI_HCD
 	select DM_MMC if MMC
+	imply CMD_FPGA_LOADMK
 
 config XTENSA
 	bool "Xtensa architecture"