[u-boot] Update to U-Boot upstream v2013.10

This change applies to overo, duovero and pepper machines. Older
versions of u-boot are removed.

Note: As u-boot has moved to SPDX license identifiers, we use the
      identifier in the README as the LIC_FILE_CHECKSUM.
[linux-gumstix] Update Overo kernel atop 3.5.7

This adds two backported patches to support recent (4.7/4.8) versions
of GCC.  A few patches were reordered based on the commit order in
github.com/gumstix/linux.git.
[linux-gumstix] Based DuoVero kernel on mainline

The DuoVero kernel uses v3.6.11 from linux-stable along with
a few patches.
[linux-gumstix] Rename kernel recipe for Pepper

Pepper uses a non-mainline kernel.  Rename this recipe to allow
for a mainline-based 3.2 kernel version.
[linux-gumstix] Add an Overo 3.2 Kernel Recipe

Some binary components for the OMAP3 series work with the 3.2 kernel.
This adds a non-default 3.2 kernel for Overo for those using SGX etc.
[u-boot] Update u-boot 2013.10 with patches from gumstix-github