console: Only add non-stub code to romstage if SEPARATE_ROMSTAGE=y

If both CONFIG_SEPARATE_ROMSTAGE and CONFIG_BOOTBLOCK_CONSOLE are not
set, compilation will fail with errors indicating redefinitions of
various console methods.

When BOOTBLOCK_CONSOLE is not set, the __CONSOLE_ENABLE__ macro in
include/console/console.h evaluates to zero when compiling the
bootblock, resulting in various console methods being defined as stubs
in the header. In a typical build with a separate bootblock and
romstage, this will not cause a conflict as the non-stub definitions
found in the console/*.c files are added conditionally to the bootblock
depending on CONFIG_BOOTBLOCK_CONSOLE.

When SEPARATE_ROMSTAGE is not set, the list of romstage objects gets
added to the bootblock. Since the console sources were unconditionally
added to romstage, the non-stub definitions were able to slip into the
bootblock, causing a redefinition of the stubs.

Avoid this by conditionally adding these sources to romstage depending
on CONFIG_SEPARATE_ROMSTAGE. If SEPARATE_ROMSTAGE is set, the non-stub
definitions are handled in the same way as they were before. If it is
not set, the union of bootblock and romstage objects will only include
the non-stub definitions based on CONFIG_BOOTBLOCK_CONSOLE, which uses
existing console/Makefile.mk rules for the bootblock.

TEST=qemu-i440fx builds successfully with all possible settings of
CONFIG_SEPARATE_ROMSTAGE and CONFIG_BOOTBLOCK_CONSOLE.

Change-Id: I59b3f0c52a4338b1573e0a647bc16cec4943fd7f
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83088
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/console/Makefile.mk

@@ -24,8 +24,8 @@ verstage-y += die.c
 verstage-y += init.c
 verstage-y += vtxprintf.c vsprintf.c
 
-romstage-y += vtxprintf.c printk.c vsprintf.c
-romstage-y += init.c console.c
+romstage-$(CONFIG_SEPARATE_ROMSTAGE) += vtxprintf.c printk.c vsprintf.c
+romstage-$(CONFIG_SEPARATE_ROMSTAGE) += init.c console.c
 romstage-y += post.c
 romstage-y += die.c