greybus: move is_gb_* functions out of greybus.h

greybus: move is_gb_* functions out of greybus.h

The functions below are only used within the context of
drivers/greybus/core.c, so move them all into core and drop their 'inline'
specifiers:

is_gb_host_device(), is_gb_module(), is_gb_interface(), is_gb_control(),
is_gb_bundle() and is_gb_svc().

Suggested-by: Alex Elder <elder@ieee.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Reviewed-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20240226-device_cleanup-greybus2-v1-1-5f7d1161e684@marliere.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>