cmd: cat: add new command

Add cat command to print file content to standard out

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Roger Knecht <rknecht@pm.me>
diff --git a/configs/sandbox64_defconfig b/configs/sandbox64_defconfig
index b20b181..0926e92 100644
--- a/configs/sandbox64_defconfig
+++ b/configs/sandbox64_defconfig
@@ -22,6 +22,7 @@
 CONFIG_CONSOLE_RECORD_OUT_SIZE=0x1000
 CONFIG_PRE_CONSOLE_BUFFER=y
 CONFIG_DISPLAY_BOARDINFO_LATE=y
+CONFIG_CMD_CAT=y
 CONFIG_CMD_CPU=y
 CONFIG_CMD_LICENSE=y
 CONFIG_CMD_BOOTZ=y