platform/x86: dell-smbios: Link all dell-smbios-* modules together

Some race conditions were raised due to dell-smbios and its backends
not being ready by the time that a consumer would call one of the
exported methods.

To avoid this problem, guarantee that all initialization has been
done by linking them all together and running init for them all.

As part of this change the Kconfig needs to be adjusted so that
CONFIG_DELL_SMBIOS_SMM and CONFIG_DELL_SMBIOS_WMI are boolean
rather than modules.

CONFIG_DELL_SMBIOS is a visually selectable option again and both
CONFIG_DELL_SMBIOS_WMI and CONFIG_DELL_SMBIOS_SMM are optional.

Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
[dvhart: Update prompt and help text for DELL_SMBIOS_* backends]
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>