boards: shields: Introduce inventek es-WIFI shield

Add Inventek es-WIFI modules shield.  This shield exposes es-WIFI driver
using Arduino Uno R3 header by UART or SPI interfaces.  It shows how
user can create their own overlay and expose es-WIFI driver.

The current Inventek's EVB doesn't have all pins necessary to control
the module by Arduino hearder.  This shows how to wire to get ISM43xx
EVB working.

Signed-off-by: Gerson Fernando Budke <gerson.budke@atl-electronics.com>
diff --git a/CODEOWNERS b/CODEOWNERS
index 81c1ab5..635c7cc 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -129,6 +129,7 @@
 /boards/shields/                          @erwango
 /boards/shields/atmel_rf2xx/              @nandojve
 /boards/shields/esp_8266/                 @nandojve
+/boards/shields/inventek_eswifi/          @nandojve
 /boards/x86/                              @andrewboie @nashif @jenmwms @aasthagr
 /boards/xtensa/                           @nashif @dcpleung
 /boards/xtensa/intel_s1000_crb/           @sathishkuttan @dcpleung