arm: defconfig: Disable serial device bus

This change disables serial bus support. This is not really needed
for UART driver but unwantedly it makes probe time driver resume
calls.

Change-Id: Ia3c6fd68e6a2091685cac37f6c22705629fe386e
Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>