x86: apl: Add PUNIT driver

Add a driver for the Apollo Lake P-unit (power unit). It is modelled as a
syscon driver since it only needs to be probed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/apollolake/Makefile b/arch/x86/cpu/apollolake/Makefile
index 36eefcb..875d454 100644
--- a/arch/x86/cpu/apollolake/Makefile
+++ b/arch/x86/cpu/apollolake/Makefile
@@ -3,6 +3,9 @@
 # Copyright 2019 Google LLC
 
 obj-$(CONFIG_SPL_BUILD) += systemagent.o
+ifndef CONFIG_TPL_BUILD
+obj-y += punit.o
+endif
 
 obj-y += hostbridge.o
 obj-y += itss.o