bq20z75: Add MODULE_DEVICE_TABLE

The device table is required to load modules based on modaliases.
After adding the MODULE_DEVICE_TABLE, below entry will be added to
modules.alias:
alias i2c:bq20z75 bq20z75

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>