drivers/pc80/pc/Makefile: use all_x86 make target

Use the newly introduced 'all_x86' make target to add the compilation
unit to all stages that run on the x86 cores, but not to verstage on
PSP.

TEST=Timeless build for Mandolin results in identical image.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I23c6977ae8acebb8dcd546f86f7f7b677272a6cb
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74153
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/drivers/pc80/pc/Makefile.inc

@@ -6,11 +6,7 @@ ramstage-y += keyboard.c
 ramstage-$(CONFIG_SPKMODEM) += spkmodem.c
 romstage-$(CONFIG_SPKMODEM) += spkmodem.c
 
-bootblock-y += i8254.c
-verstage_x86-y += i8254.c
-romstage-y += i8254.c
-ramstage-y += i8254.c
-postcar-y += i8254.c
+all_x86-y += i8254.c
 smm-y += i8254.c
 
 endif