soc: esp32: XIP removed from Espressif targets

The way ESP32 XIP works (with MMU and cache) does no fit the way Zephyr XIP
is implemented, causing issues related to included Zephyr linker files.
Flash code still resides in flash for execution, but MMU/Cache handles it
in such way that XIP might not (or should not) be used with current Zephyr
approach. To address this problem, XIP configuration option is being
removed from Espressif targets.

Signed-off-by: Marcio Ribeiro <marcio.ribeiro@espressif.com>