[ALPS08797255] uart: m6989: fix apdma devapc issue

[Description]
1. Do error handling when polling apdma tx fail.
2. Add mutex lock in dump info API to avoid access null pointer after
multi-thread free dma channel.
3. update uart shutdown flow to fix devapc issue.

[Test]
Build pass and BT on/off stress pass.

MTK-Commit-Id: a82cee2e766ad2cf45b43e2b91258cf27098d7e1

Signed-off-by: lucky.dong <lucky.dong@mediatek.com>
CR-Id: ALPS08797255
Feature: uart_driver
Change-Id: I09444ea220a9adaf0b5f7d61d37807c0757f72e3