ARM: display5: Remove common.c file (after DM/DTS U-Boot proper conversion)

The common.c file content can be safely moved to spl.c file after
performing the DM/DTS conversion for the U-Boot proper.

It contains the non DM/DTS setup code, which now is only used by SPL.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
diff --git a/board/liebherr/display5/Makefile b/board/liebherr/display5/Makefile
index f934672..ee503ad 100644
--- a/board/liebherr/display5/Makefile
+++ b/board/liebherr/display5/Makefile
@@ -5,7 +5,7 @@
 # SPDX-License-Identifier:    GPL-2.0+
 #
 ifdef CONFIG_SPL_BUILD
-obj-y = common.o spl.o
+obj-y = spl.o
 else
-obj-y := common.o display5.o
+obj-y := display5.o
 endif