ppc: Drop unused CONFIG_P2020DS

This option does not exist, so the Makefile rule does nothing. Drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/freescale/common/Makefile b/board/freescale/common/Makefile
index fc51d6d..9d5f38b 100644
--- a/board/freescale/common/Makefile
+++ b/board/freescale/common/Makefile
@@ -54,7 +54,6 @@
 
 obj-$(CONFIG_TARGET_MPC8536DS)	+= ics307_clk.o
 obj-$(CONFIG_TARGET_P1022DS)		+= ics307_clk.o
-obj-$(CONFIG_P2020DS)		+= ics307_clk.o
 obj-$(CONFIG_TARGET_P3041DS)		+= ics307_clk.o
 obj-$(CONFIG_TARGET_P4080DS)		+= ics307_clk.o
 obj-$(CONFIG_TARGET_P5040DS)		+= ics307_clk.o