Add gpio-presence-sensor

This is to implement the gpio based hw inventory design [1].

There is a new meson option 'gpio-presence' to enable/disable the
daemon.

Summary of the functionality:

- fet

Add gpio-presence-sensor

This is to implement the gpio based hw inventory design [1].

There is a new meson option 'gpio-presence' to enable/disable the
daemon.

Summary of the functionality:

- fetch configuration from EM, according to the configuration interface
- the D-Bus interface is
xyz.openbmc_project.Configuration.GPIODeviceDetect
- the configuration represents devices for which presence can be
detected based on gpio values.
- watch gpios for changes
- add/remove the xyz.openbmc_project.Inventory.Source.DevicePresence
interface on the object path based on gpio values.

References:
[1] https://github.com/openbmc/docs/blob/master/designs/inventory/gpio-based-hardware-inventory.md
[2] https://www.kernel.org/doc/html/latest/admin-guide/gpio/gpio-sim.html

Tested: using linux gpio-sim facility, see below

1. create a fake gpio via [2]
2. configure gpio-presence-sensor as per [1]
3. run the gpio-presence-sensor
4. change the value of the gpio previously configured
5. there should be log output (at debug level)
6. the dbus interfaces exposed should appear/disappear as per [1]

Change-Id: I4cf039b583247581aa5c6c6c59e7fc41ced0bb85
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>

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