platform/x86: dell-smbios: Rename dell-smbios source to dell-smbios-base

This is being done to faciliate a later change to link all the dell-smbios
drivers together.

Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>