Revert "Merge pull request #241 from bright-pan/master"

This reverts commit 5aeedc4f3a3c3fcfffb0cd4a474f5faa75053839, reversing
changes made to 3d80e414ff6c03ff04fecb914e7aa9b3fb535e03.

This merge breaks every uart driver in all BSPs. @bright-pan , is there
any way to get this done without breaking existing code?
Merge pull request #243 from grissiom/serial-rollback

Revert "Merge pull request #241 from bright-pan/master"