boards: esp32xx: update BT heap of all espressif boards

Current internal BT heap uses custom heap area, which reserves
unused RAM area. In order to free up some RAM, BT HAL
implementation was changed to use sysheap instead.
With this change, something around ~13kb is now available for
application, optmizing RAM usage.

Signed-off-by: Sylvio Alves <sylvio.alves@espressif.com>