efi: app: Enable the cat command

This can be handy for looking at extlinux.conf files, so enable it for
the app.

Series-to: concept
Series-version: 2
Cover-letter:
efi: Improvements for the EFI app on ARM
This series provides a number of minor improvements for the EFI app when
running on ARM machines (on top of Tianocore, for example):

- Tidy up various comments
- Show the ARM exception level in bdinfo
- Tidy up the output of 'meminfo'
- Get the addr_find command running
- Reduce verbosity when not debugging
- Show the model at the top of the diplay when using vidconsole
- Allow faking the boot right into the actual OS jump (for debugging)
END

Signed-off-by: Simon Glass <sjg@chromium.org>

configs/efi-arm_app64_defconfig

@@ -29,6 +29,7 @@ CONFIG_CMD_MEMINFO=y
 CONFIG_CMD_MEMINFO_MAP=y
 CONFIG_CMD_DM=y
 CONFIG_CMD_LSBLK=y
+CONFIG_CMD_CAT=y
 CONFIG_CMD_CACHE=y
 CONFIG_CMD_TIME=y
 CONFIG_CMD_EXT4_WRITE=y