boards: esp32xx: Use common partition tables

* Replace copies of fixed-partitions nodes in related boards by
referencing the apropriate partition table from the available list.
* For better reference the `partitions_*.dtsi` file has boot offset,
purpose and the flash size encoded in the file name. Default flash size
is considered to be 4MB.
* Added the flash size node for the boards which are not based on the
module.
* Removed flash size registry from the esp32.*common.dtsi

Signed-off-by: Marek Matej <marek.matej@espressif.com>