boards: nordic: nrf54l15dk: Fix references to pdk

A bunch of copy-paste mistakes when adding the nRF54L15 DK added stale
references to the Preview DK (PDK).

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>

boards/nordic/nrf54l15dk/doc/index.rst

@@ -101,7 +101,7 @@ to be built as multicore configuration with code snippet called ``vpr_launcher``
 for the application core.
 
 Enter the following command to compile ``hello_world`` for the FLPR core::
- west build -p -b nrf54l15pdk/nrf54l15/cpuflpr --sysbuild -- -DSB_VPR_LAUNCHER=y
+ west build -p -b nrf54l15dk/nrf54l15/cpuflpr --sysbuild -- -DSB_VPR_LAUNCHER=y
 
 Flashing
 ========

tests/boards/nrf/qdec/boards/nrf54l15dk_nrf54l15_cpuapp.overlay

@@ -3,7 +3,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-#include "nrf54l15pdk_nrf54l15_common.dtsi"
+#include "nrf54l15dk_nrf54l15_common.dtsi"
 
 /* To prevent enabling console receiver. */
 &uart20 {

tests/boards/nrf/qdec/boards/nrf54l15dk_nrf54l15_cpuflpr.overlay

@@ -3,7 +3,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-#include "nrf54l15pdk_nrf54l15_common.dtsi"
+#include "nrf54l15dk_nrf54l15_common.dtsi"
 
 /* To prevent enabling console receiver. */
 &uart30 {

tests/drivers/counter/counter_basic_api/boards/nrf54l15bsim_nrf54l15_cpuapp.overlay

@@ -1 +1 @@
-#include "nrf54l15pdk_nrf54l15_cpuapp.overlay"
+#include "nrf54l15dk_nrf54l15_cpuapp.overlay"

tests/drivers/spi/spi_controller_peripheral/README.txt

@@ -2,7 +2,7 @@ In this test suite two instances of the SPI peripheral are connected together.
 One SPI instance works as a controller, second one is configured as a peripheral.
 In each test, both instances get identical configuration (CPOL, CPHA, bitrate, etc.).
 
-Four GPIO loopbacks are required (see overlay for nrf54l15pdk for reference):
+Four GPIO loopbacks are required (see overlay for nrf54l15dk for reference):
 1. spi22-SPIM_SCK connected with spi21-SPIS_SCK,
 2. spi22-SPIM_MISO connected with spi21-SPIS_MISO,
 3. spi22-SPIM_MOSI connected with spi21-SPIS_MOSI,