Add armhf support for cross compilation

[jedahan]

So I tried cross compiling using the readme

cross build --target=arm-unknown-linux-gnueabi --release --example raspberry_pi_inky_phat --features examples

And a binary did result, but segfaulted on my raspberry pi zero w. The resulting file format is:

ELF 32-bit LSB pie executable ARM, EABI5 version 1 (SYSV), dynamically linked, 
interpreter /lib/ld-linux.so.3, for GNU/Linux 2.6.32, 
BuildID[sha1]=106da3de504ff660e85093b399132de00f484060, with debug_info, not stripped

When I tried using gnueabihf, and pointed the cross tool to rustcross/arm-unknown-linux-gnueabihf, the resulting file format is:

ELF 32-bit LSB pie executable ARM, EABI5 version 1 (SYSV), dynamically linked, 
interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 2.6.26, BuildID[sha1]=e7943ad7ed53c12c384d60981761686e6468658f, with debug_info, not stripped

I am new to cross compiling, so I am not sure if this is some other problem with my pi, but would you mind trying out both and seeing if this is helpful?

[codecov-io]

Codecov Report

Merging #7 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #7   +/-   ##
=======================================
  Coverage   91.66%   91.66%           
=======================================
  Files           5        5           
  Lines         192      192           
=======================================
  Hits          176      176           
  Misses         16       16

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[wezm]

I discovered this myself preparing my linux.conf.au project but hadn’t updated the project yet. Thanks for the PR