efi: Add esrt support

Add sysfs files for the EFI System Resource Table (ESRT) under
/sys/firmware/efi/esrt and for each EFI System Resource Entry under
entries/ as a subdir.

The EFI System Resource Table (ESRT) provides a read-only catalog of
system components for which the system accepts firmware upgrades via
UEFI's "Capsule Update" feature.  This module allows userland utilities
to evaluate what firmware updates can be applied to this system, and
potentially arrange for those updates to occur.

The ESRT is described as part of the UEFI specification, in version 2.5
which should be available from http://uefi.org/specifications in early
2015.  If you're a member of the UEFI Forum, information about its
addition to the standard is available as UEFI Mantis 1090.

For some hardware platforms, additional restrictions may be found at
http://msdn.microsoft.com/en-us/library/windows/hardware/jj128256.aspx ,
and additional documentation may be found at
http://download.microsoft.com/download/5/F/5/5F5D16CD-2530-4289-8019-94C6A20BED3C/windows-uefi-firmware-update-platform.docx
.

Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>