device: give device state variables a linker section

This groups the device state variables in their own linker section.
This is needed for demand paging as these variables are needed
during boot where the paging mechanism has not been initialized.
These variables need to be in the pinned section so they can
be accessed during boot.

Note that if device PM is not enabled, the device state variables
are put into BSS. So we need to pin these.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>