iio: imu: inv_mpu6050: Create mux clients for ACPI

This is a follow up patches after adding i2c mux adapter for bypass
mode. Potentially many different types of sensor can be attached to
INVMPU6XXX device, which can be connected to main cpu i2c bus in
bypass mode.
Why do we need this?
The system ACPI table entry will consist of only one device for
INV6XXX, assuming that this driver will handle all connected sensors.
That is not true for the Linux driver. There are bunch of IIO drivers
for each sensors, hence we created a mux on this device. So to load
these additional drivers, we need to create i2c devices for them
in this driver using this mux adapter.

There are multiple options:
1. Use the auto detect feature, this needs a new i2c class for the
adapter as the existing HWMON class is not acceptable. Also the
autodetect has overhead of executing detect method for each
matching class of adapters.
This is a simple implementation. This option was previously submitted
with not a happy feedback.

2. Option is use ACPI magic and parse the configuration data. What
we need to create a i2c device at a minimum is address and a name.
Address can be obtained for secondary device in more or less in a
standard way from using _CRS element. But there is no name. To get
name we need to process proprietary vendor data. Not having name is
not fun, as you have to create device using the device name of
INVN6XXXX, respecting driver duplicate name space restriction.
Also each client driver needs to have this name in the id table.
Since multiple driver can be loaded, the driver should be able to
detect its presence and gracefully exit for the other client driver
to take it over.
So we use two step process:
- Use DMI to id platform and parse propritery data. This is not uncommon
for many x86 platform specific driver. We will get both name and address.
The change created necessary infrastructure to add more properitery vendor
data parsing.
- If DMI match fails, then create device on INV6XXX-client (we can't
create with same name as INV6XXX as it will cause duplicate name and driver
model will reject.) With this each client sensor driver which needs to get
attached via INV6XXXX, need this name in the id table and detect the
physical presence of sensor in probe and exit if not found.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

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