Convert CONFIG_SHOW_BOOT_PROGRESS to Kconfig

This converts the following to Kconfig:
   CONFIG_SHOW_BOOT_PROGRESS

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/am335x_shc_netboot_defconfig b/configs/am335x_shc_netboot_defconfig
index fdb22af..c526cd5 100644
--- a/configs/am335x_shc_netboot_defconfig
+++ b/configs/am335x_shc_netboot_defconfig
@@ -15,6 +15,7 @@
 CONFIG_SHC_NETBOOT=y
 CONFIG_SERIES=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SHOW_BOOT_PROGRESS=y
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_DEFAULT_FDT_FILE="am335x-shc"