ti-cgt-pru: add package for PRU Host toolchain

ti-cgt-pru: add package for PRU Host toolchain

TI provides a binary code generation toolchain to develop firmware for
the programmable real-time unit/co-processor found in some SOCs such as
some models in the AM335x line. This toolchain includes C/C++ support
(clpru) rather than just assembler (pasm) supported by the pre-existing
am335x-pru-package [1].  Following the lead of the Yocto meta-ti
layer [2], this package provides a host toolchain suitable for an x86
(or x86_64) Linux targeting an ARM-based PRU core.

[1] http://processors.wiki.ti.com/index.php/PRU_Assembly_Instructions#pasm_vs._clpru
[2] http://git.yoctoproject.org/cgit/cgit.cgi/meta-ti/tree/recipes-ti/devtools/ti-cgt-pru_2.1.1.bb

Signed-off-by: Ash Charles <ash.charles@savoirfairelinux.com>
[Thomas: add BR2_PACKAGE_HOST_TI_CGT_PRU_ARCH_SUPPORTS boolean option,
so that packages selecting host-ti-cgt-pru can easily inherit its
architecture dependencies.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>