spelling: add ignore list

Thu Ba reported that their name is getting rejected as a spelling
mistake in their Signed-off-by.  Add capability to ignore words
from the primary dictionaries and add 'ba' to the ignore list.

Tested:

Before change, manually running codespell results in:
```
./config/openbmc-spelling-ignore.txt:1: Ba ==> By, be
```
Manually running codespell with ignore-list option removes this.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I33134e519e28024926b6da00340d2d52e2e884bd
3 files changed