x86: disable X2APIC support for legacy subtargets

Explicitely disable X2APIC support on legacy targets since the targeted
processor types do not support it anyway there.

Fixes FS#285.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/x86/geode/config-default

@@ -141,3 +141,4 @@ CONFIG_X86_DEBUGCTLMSR=y
 CONFIG_X86_PM_TIMER=y
 CONFIG_X86_REBOOTFIXUPS=y
 CONFIG_X86_TSC=y
+# CONFIG_X86_X2APIC is not set

target/linux/x86/legacy/config-default

@@ -226,3 +226,4 @@ CONFIG_X86_ACPI_CPUFREQ=y
 # CONFIG_X86_PCC_CPUFREQ is not set
 CONFIG_X86_PM_TIMER=y
 # CONFIG_X86_POWERNOW_K8 is not set
+# CONFIG_X86_X2APIC is not set