rpi-config: Check some config values against "1"
rpi-config: Check some config values against "1"

When we read the docs, we have the feelings that theses variables are
boolean ones. So I was setting, for example in my distro.conf file the
variable ' ENABLE_I2C = "1" ' to enable I2C. Then I wanted to disable it
by simply setting 'ENABLE_I2C' to "0" but it wasn't working. So I
noticed that, for example, ' ENABLE_UART ' was checked with ' = "1" '
condition and some other "boolean" was checked against ' -n ' like for
ENABLE_I2C.

This commit tries to have an uniform behavior for all variables that are
shown in the doc under the format ' VARIABLE = "1" ' to enable them and
the reader can think they are kind of 'boolean' values.

Signed-off-by: Joël Carron <484aca816b2e1b7b3fbb1787ab84078b14901db8@eeproperty.ch>

agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,leon-anavi/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,leon-anavi/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi