defconfig: arm64: bengal: Decide UART sampling rate based on config

Clock divider needs to get doubled for QUP HW version greater
than 2.5.0 as sampling rate is half. As earlycon can't have HW
version awareness, decision is taken based on the configuration.

Change-Id: I9abc2d6b25b0c1bfd4a94baaebfb75f0beb92974
Signed-off-by: Akash Asthana <akashast@codeaurora.org>