The error message for Z_DEVICE_NAME_CHECK was needlessly calling
DEVICE_NAME_GET() on the "name" string, resulting in a confusing message
being displayed.

Remove the DEVICE_NAME_GET call so that the error message shown by the
compiler contains the actual name.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

The comment for Z_DEVICE_DT_DEV_ID() is misleading: device_get_binding()
compares its inputs with values generated by the DEVICE_DT_NAME() macro,
which expands to the node's DT label or to the node's full name.

This patch updates the comment to reflect the actual behavior of
Z_DEVICE_DT_DEV_ID().

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

This patch adds an indirection level moving the current code from inside
the EXPORT_SYMBOL and LL_EXTENSION_SYMBOL macros to private Z_* macros.
This is done to allow for the official APIs to properly expand more
complex arguments, such as the DT function-like macros.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

This change adds a new configuration option, LLEXT_EXPORT_DEVICES, which
enables exporting all devices defined in the device tree to llext
extensions. When enabled, all devices are made available to extensions
via the standard DT_ / DEVICE_* macros.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

Add a new test to the simple llext test suite that verifies that DT
devices are properly exported to extensions. This is done by obtaining a
device handle from the DT and then trying to get the same handle at
runtime using the device_get_binding() API.

This test is optional because the current qemu_xtensa platform does not
have any usable DT devices to test with.

The LLEXT heap size is also increased to 64 kbytes to avoid heap
exhaustion when running the new test on mps2_an385.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>