Provide option to always use device path

The application has the ability to use either the 'OF_FULLNAME' udev
environment variable or the udev device path as the path to the config
file, though it d

Provide option to always use device path

The application has the ability to use either the 'OF_FULLNAME' udev
environment variable or the udev device path as the path to the config
file, though it defaults to OF_FULLNAME if it's there.

The disadvantage of using OF_FULLNAME is that the file name then has to
match what someone manually typed into the device tree for the system,
for example mydevice@72.conf. The device path method, on the other
hand, has a file name that matches the stable I2C details, such as
7-0052.conf.

To force phosphor-hwmon to always use the device path for its config and
avoid being dependent on the device tree name, this commits adds a new
--always-use-devpath meson option.

When enabled, it add an '|| true' into the start_hwmon.sh script to
force it down the path to use the device path when starting the hwmon
service.

Tested:
When disabled, diffed start_hwmon.sh to that built from previous HEAD
and the files matched.

When enabled, start_hwmon.sh now has
```
if [ -z "${path}" ] || true
```

and app now uses device path for config file path.

Change-Id: I5a03ebb6e6e967bc663ec747941258173dfd3363
Signed-off-by: Matt Spinler <spinler@us.ibm.com>

show more ...

meson_options.txt: Support for reading options from meson.options

Support has been added for reading options from meson.options instead
of meson_options.txt[1]. These are equivalent, but not using t

meson_options.txt: Support for reading options from meson.options

Support has been added for reading options from meson.options instead
of meson_options.txt[1]. These are equivalent, but not using the .txt
extension for a build file has a few advantages, chief among them
many tools and text editors expect a file with the .txt extension to
be plain text files, not build scripts.

[1] https://mesonbuild.com/Release-notes-for-1-1-0.html#support-for-reading-options-from-mesonoptions

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I978909ddffdb49550bb4f265ff2bbfc96fec4fa6

show more ...