bubblegum.conf: switch tune to cortexa53
bubblegum.conf: switch tune to cortexa53

Switch to use a Cortex A53 tune file as it is now available in OE-Core.

Signed-off-by: Ricardo Salveti <d4e7430f1534a12df46cedd1ac369935436dbb94@foundries.io>

mrchapp/meta-96boards,96boards/meta-96boards