greybus: arche-platform: Rename db3-platform to arche-platform

With multiple platforms getting rolled into ara,
db3 name is confusing. And this driver is applicable
to all arche platforms, so make sense to rename it to
arche-platform.c. Also rename all internal functions
accordingly.

Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>