[coreboot] PATCH: Tidy up (and backport) all cs5536 uart initiation

[Edwin Beasant]

This patch backports the AMD CS5536 early UART config from v3 to v2/v4:
-        Assorted comment tidyups
-        Com2 Early enable now permitted
Tested on a 'Norwich' *type* board

Signed-off-by: Edwin Beasant