x86: clean up apic->acpi_madt_oem_check methods

Impact: refactor code

x86 subarchitectures each defined a "acpi_madt_oem_check()" method,
which could be an inline function, or an extern, or a static function,
and which was also the name of a genapic field.

Untangle this namespace spaghetti by setting ->acpi_madt_oem_check()
to NULL on those subarchitectures that have no detection quirks,
and rename the other ones (summit, es7000) that do.

Also change default_acpi_madt_oem_check() to handle NULL entries,
and clean its control flow up as well.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/mach-generic/default.c b/arch/x86/mach-generic/default.c
index d5fec76..cfec349 100644
--- a/arch/x86/mach-generic/default.c
+++ b/arch/x86/mach-generic/default.c
@@ -28,7 +28,7 @@
 
 	.name				= "default",
 	.probe				= probe_default,
-	.acpi_madt_oem_check		= acpi_madt_oem_check,
+	.acpi_madt_oem_check		= NULL,
 	.apic_id_registered		= apic_id_registered,
 
 	.int_delivery_mode		= INT_DELIVERY_MODE,