tests: drivers: uart: uart_pm: Limit scope for nrf54l15

Some configurations which are not valid for nrf54l15. Mainly those
which are using ENHANCED_POLL_OUT option which is not applicable for
nrf54l15 because it has ENDTX_STOPTX short so PPI connection is not
needed.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

tests/drivers/uart/uart_pm/testcase.yaml

@@ -5,6 +5,7 @@ common:
   harness: ztest
   platform_allow:
     - nrf52840dk/nrf52840
+    - nrf54l15pdk/nrf54l15/cpuapp
     - nrf52_bsim
   harness_config:
     fixture: gpio_loopback
@@ -24,6 +25,8 @@ tests:
       - CONFIG_UART_0_ENHANCED_POLL_OUT=n
       - CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=y
     extra_args: DTC_OVERLAY_FILE="boards/nrf52840dk_nrf52840.overlay;nrf_rx_disable.overlay"
+    platform_exclude:
+      - nrf54l15pdk/nrf54l15/cpuapp
 
   drivers.uart.pm.enhanced_poll:
     extra_configs:
@@ -31,6 +34,8 @@ tests:
       - CONFIG_UART_ASYNC_API=n
       - CONFIG_UART_0_ENHANCED_POLL_OUT=y
       - CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=y
+    platform_exclude:
+      - nrf54l15pdk/nrf54l15/cpuapp
 
   drivers.uart.pm.int_driven:
     extra_configs:
@@ -47,6 +52,8 @@ tests:
       - CONFIG_UART_ASYNC_API=n
       - CONFIG_UART_0_ENHANCED_POLL_OUT=y
       - CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=y
+    platform_exclude:
+      - nrf54l15pdk/nrf54l15/cpuapp
 
   drivers.uart.pm.async:
     extra_configs:
@@ -69,3 +76,5 @@ tests:
       - CONFIG_NRFX_TIMER2=y
       - CONFIG_UART_0_ENHANCED_POLL_OUT=y
       - CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=y
+    platform_exclude:
+      - nrf54l15pdk/nrf54l15/cpuapp