i2c: Use IS_REACHABLE() for substituting empty ACPI functions

i2c: Use IS_REACHABLE() for substituting empty ACPI functions

Replace IS_ENABLED() with IS_REACHABLE() to substitute empty stubs for:
    i2c_acpi_get_i2c_resource()
    i2c_acpi_client_count()
    i2c_acpi_find_bus_speed()
    i2c_acpi_new_device_by_fwnode()
    i2c_adapter *i2c_acpi_find_adapter_by_handle()
    i2c_acpi_waive_d0_probe()

commit f17c06c6608a ("i2c: Fix conditional for substituting empty ACPI
functions") partially fixed this conditional to depend on CONFIG_I2C,
but used IS_ENABLED(), which is wrong since CONFIG_I2C is tristate.

CONFIG_ACPI is boolean but let's also change it to use IS_REACHABLE()
to future-proof it against becoming tristate.

Somehow despite testing various combinations of CONFIG_I2C and CONFIG_ACPI
we missed the combination CONFIG_I2C=m, CONFIG_ACPI=y.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: f17c06c6608a ("i2c: Fix conditional for substituting empty ACPI functions")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202408141333.gYnaitcV-lkp@intel.com/
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>