UART include error

[nimishgautam]

When I try to compile including the UART driver in chibios, I get an error error: 'A9' undeclared and a cascade of other errors about undefined constants and functions.

Simply adding #include "quantum.h" at the top of platforms/chibios/drivers/uart.c fixes all these errors, but I noticed that line was specifically removed from the file in this commit from @fauxpark :b6d9409 so I assume it's supposed to be included somewhere else but I couldn't find where.

(The code is from a third-party vendor that's not in the main vial branch, I have modified their included source in a personal repo here: https://github.com/nimishgautam/qmk-staging/tree/main/w_corne/w_corne/keymaps/nimishgautam, it may contain other errors but I couldn't get UART successfully included in any way without adding the above back in)