ARM: dts: aspeed: bletchley: add sample averaging for ADM1278

set number of sample averaging to 128 for both PWR_AVG and VI_AVG

Signed-off-by: Potin Lai <potin.lai@quantatw.com>
Reviewed-by: Patrick Williams <patrick@stwcx.xyz>
Link: https://lore.kernel.org/r/20220418094827.6185-1-potin.lai@quantatw.com
Signed-off-by: Joel Stanley <joel@jms.id.au>