Feature/rpi3 (#98)

* Add rpi3-64 defconfig file

* Work on getting RPI3 into shape

* Merge latest rpi3 changes into rpi4 config

buildroot-external/board/raspberrypi3-64/meta

@@ -0,0 +1,3 @@
+BOARD_ID=rpi3-64
+BOARD_NAME="RaspberryPi 3 64bit"
+CHASSIS=embedded

buildroot-external/board/raspberrypi3-64/rootfs-overlay/home/mycroft/.local/share/precise03/christopher-precise.pb.params

@@ -0,0 +1 @@
+{"window_t": 0.1, "hop_t": 0.05, "buffer_t": 1.5, "sample_rate": 16000, "sample_depth": 2, "n_mfcc": 13, "n_filt": 20, "n_fft": 512}

buildroot-external/board/raspberrypi3-64/rootfs-overlay/home/mycroft/.local/share/precise03/hey-mycroft-2.pb.params

@@ -0,0 +1 @@
+{"window_t": 0.1, "hop_t": 0.05, "buffer_t": 1.5, "sample_rate": 16000, "sample_depth": 2, "n_mfcc": 13, "n_filt": 20, "n_fft": 512, "use_delta": false}