defconfig: disable more random debug and tests

Disable console output during boot: This will suppress printk output
during boot to speed up kernel boot time. Note that printk messages
are still buffered in the kernel and can be retrieved after booting
using the "dmesg" command.

Also disable DEBUG_MUTEXES

Change-Id: I2f70a5e911a3f71c482279eaf471d92e8b4ecf4c