cpu/x86: Introduce and use CPU_X86_LAPIC

With using a Kconfig option to add the x86 LAPIC support code to the
build, there's no need for adding the corresponding directory to subdirs
in the CPU/SoC Makefile. Comparing which CPU/SoC Makefiles added
(cpu/)x86/mtrr and (cpu/)x86/lapic before this and the corresponding
MTRR code selection patch and having verified that all platforms
added the MTRR code on that patch shows that soc/example/min86 and
soc/intel/quark are the only platforms that don't end up selecting the
LAPIC code. So for now the default value of CPU_X86_LAPIC is chosen as y
which gets overridden to n in the Kconfig of the two SoCs mentioned
above.

Change-Id: I6f683ea7ba92c91117017ebc6ad063ec54902b0a
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44228
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

src/soc/intel/quark/Kconfig

@@ -24,6 +24,10 @@ config CPU_SPECIFIC_OPTIONS
 	select USE_MARCH_586
 	select NO_SMM
 
+config CPU_X86_LAPIC
+	bool
+	default n
+
 #####
 # Debug serial output
 #     The following options configure the debug serial port