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>

arch/x86/kernel/acpi/boot.c

@@ -239,7 +239,8 @@ static int __init acpi_parse_madt(struct acpi_table_header *table)
 		       madt->address);
 	}
 
-	acpi_madt_oem_check(madt->header.oem_id, madt->header.oem_table_id);
+	default_acpi_madt_oem_check(madt->header.oem_id,
+				    madt->header.oem_table_id);
 
 	return 0;
 }