arch/ppc64: Pass cbmem_top to ramstage via calling argument

This avoids the need for a platform specific implementation of
cbmem_top.

HOW TO TEST? There is no serial console for the qemu target...

Change-Id: I68aa09a46786eba37c009c5f08642445805b08eb
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36276
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marty E. Plummer <hanetzer@startmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/arch/ppc64/Kconfig

@@ -1,5 +1,6 @@
 config ARCH_PPC64
 	bool
+	select RAMSTAGE_CBMEM_TOP_ARG
 
 config ARCH_BOOTBLOCK_PPC64
 	bool

src/arch/ppc64/include/arch/stages.h

@@ -16,6 +16,6 @@
 
 #include <main_decl.h>
 
-void stage_entry(void) __attribute__((section(".text.stage_entry")));
+void stage_entry(uintptr_t stage_arg) __attribute__((section(".text.stage_entry")));
 
 #endif

src/arch/ppc64/stages.c

@@ -22,9 +22,12 @@
  * linker script.
  */
 
+#include <cbmem.h>
 #include <arch/stages.h>
 
-void stage_entry(void)
+void stage_entry(uintptr_t stage_arg)
 {
+	if (!ENV_ROMSTAGE_OR_BEFORE)
+		_cbmem_top_ptr = stage_arg;
 	main();
 }

src/mainboard/emulation/qemu-power8/Makefile.inc

@@ -15,7 +15,6 @@
 bootblock-y += bootblock.c
 bootblock-y += uart.c
 romstage-y += cbmem.c
-ramstage-y += cbmem.c
 romstage-y += romstage.c
 ramstage-y += timer.c
 romstage-y += uart.c