platform/x86: dell-smbios: Resolve dependency error on ACPI_WMI

Similarly to DCDBAS for DELL_SMBIOS_SMM, if DELL_SMBIOS_WMI is enabled,
DELL_SMBIOS becomes dependent on ACPI_WMI. Update the depends lines to
prevent a configuration where DELL_SMBIOS=y and either backend
dependency =m. Update the comment accordingly.

Cc: Mario Limonciello <mario.limonciello@dell.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>