Enabling SPI bus automatically

[thortex]

r=`grep 'spi=on' /boot/config.txt | grep -v "^#"`
if [ "$r" != "" ] ; then
     sed -i 's/^dtparam=spi=off/dtparam=spi=on/;' /boot/config.txt
fi

Note that 'dtparam' key allow multiple parameters list:

dtparam=i2c_arm=on,spi=on