platform/x86: dell-smbios: Add a sysfs interface for SMBIOS tokens

Currently userspace tools can access system tokens via the dcdbas
kernel module and a SMI call that will cause the platform to execute
SMM code.

With a goal in mind of deprecating the dcdbas kernel module a different
method for accessing these tokens from userspace needs to be created.

This is intentionally marked to only be readable as a process with
CAP_SYS_ADMIN as it can contain sensitive information about the
platform's configuration.

While adding this interface I found that some tokens are duplicated.
These need to be ignored from sysfs to avoid duplicate files.

MAINTAINERS was missing for this driver.  Add myself and Pali to
maintainers list for it.

Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Reviewed-by: Edward O'Callaghan <quasisec@google.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>