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/xtfpga_defconfig b/configs/xtfpga_defconfig
index e95b664..deb9799 100644
--- a/configs/xtfpga_defconfig
+++ b/configs/xtfpga_defconfig
@@ -1,6 +1,7 @@
 CONFIG_XTENSA=y
 CONFIG_SYS_CPU="dc233c"
 CONFIG_XTFPGA_KC705=y
+CONFIG_SHOW_BOOT_PROGRESS=y
 CONFIG_BOOTDELAY=10
 CONFIG_MISC_INIT_R=y
 CONFIG_VERSION_VARIABLE=y