soc: espressif: esp32: add WROVER-E-N16R4 SiP variant

It seems this SiP variant is not sold by espressif directly, but it is
used by the Odroid Go. The Odroid Go documentation calls this a "custom"
model [1].

There already exists a SiP specific device tree include file:

  zephyr/dts/xtensa/espressif/esp32/esp32_wrover_e_n16r4.dtsi

[1] https://wiki.odroid.com/odroid_go/odroid_go#specifications



Signed-off-by: Gero Schwäricke <gero.schwaericke@posteo.de>