Add board esp8285_2m for generic 8285 with 2MiB flash

[nkinnan]

This file is identical to esp8285.json with two changes that bump the flash size from 1MiB to 2MiB:

The upload.maximum_size value of "2097152" is taken from modwifi.json which is another 2MiB flash board.

The build.arduino.ldscript value is modified from "eagle.flash.1m256.ld" to "eagle.flash.2m256.ld".
---- Though modwifi.json (another 2MiB board) uses "eagle.flash.2m.ld" instead of "eagle.flash.2m256.ld", I have no insight which partition layout is preferable and am choosing to mimic the 1MiB esp8285.json board definition on the assumption that this is the proper choice for a generic board.