tummiboot Simple UEFI boot manager(gummiboot) with Trusted Boot (tboot) support

This is the new functionality that tummiboot adds to the gummiboot bootloader:

- trusted boot support via the tboot module and Intel's Trusted
Execution Technology (TXT)
- partial multiboot2 support for passing data to the trusted boot module
- booting non EFI_STUB kernels via tboot and the Linux/x86 boot protocol
- no impact on the existing gummiboot functionality

A sample configuration file entry for tboot can be found below:

title Trusted Boot(tboot)
multiboot2              /tboot
multiboot2_options      /tboot loglvl=all logging=serial,vga,memory
vga_delay=1 serial=115200,8n1,0x3f8
acm                     /acm
linux                   /vmlinuz
initrd                  /initrd
options                 root=UUID=c1f42944-05fe-40eb-99b6-4b79161113b5 nomodeset
console=tty0 console=ttyS0,115200n8

By default tummiboot executes only EFI images unless trusted boot is requred.
The default entry is selected by a configured pattern (glob) or an on-screen menu.

tummiboot operates on the EFI System Partition (ESP) only. Configuration
file fragments, kernels, initrds, tboot and other EFI images need to reside on the
ESP. Linux kernels must be built with CONFIG_EFI_STUB to be able to be
directly executed as an EFI image or alternatively they can be booted with tboot
over the Linux/x86 boot protocol.

tummiboot reads simple and entirely generic configurion files; one file
per boot entry to select from.

Pressing Space (or most other) keys during bootup will show an on-screen
menu with all configured entries to select from. Pressing enter on the
selected entry loads and starts the EFI image.

If no timeout is configured and no key pressed during bootup, the default
entry is booted right away.

Further Trusted Boot (tboot) documentation is available at:
  http://sourceforge.net/projects/tboot/

Further bootloader documentation is available in the gummiboot wiki at:
  http://freedesktop.org/wiki/Software/gummiboot

Links:
  http://www.intel.co.uk/content/www/uk/en/architecture-and-technology/trusted-execution-technology/txt-enabling-guide.html
  http://www.trustedcomputinggroup.org/resources/trusted_platform_module_tpm_summary
  http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec
  http://www.freedesktop.org/software/systemd/man/kernel-install.html