meta-facebook : Add phosphor-buttons gpio config YV2

This change adds phosphor-buttons gpio configs for
the following :

1. Power button
2. Reset button
3. Host selector
4. Debug host select

meta-facebook : Add phosphor-buttons gpio config YV2

This change adds phosphor-buttons gpio configs for
the following :

1. Power button
2. Reset button
3. Host selector
4. Debug host selector button
5. serial uart mux

To keep the install method common for copying gpio_defs.json file
in supported platforms the install method is moved to
obmc-phosphor-buttons_git.bb file.

Signed-off-by: Naveen Moses <naveen.mosess@hcl.com>
Change-Id: I91a106fdc5ac9aa83eec63cbd41a9615b380c37d

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