meta-xilinx-core: Add weak preferred qemu providers

By doing so we avoid seeing following bitbake nags when
machine-xilinx-qemu.inc is not included in build configuration:

  NOTE: Multiple providers are available for qemu-native (qemu-native, qemu-xilinx-native)
  Consider defining a PREFERRED_PROVIDER entry to match qemu-native
  NOTE: Multiple providers are available for qemu-helper-native (qemu-helper-native, qemu-xilinx-helper-native)
  Consider defining a PREFERRED_PROVIDER entry to match qemu-helper-native
  NOTE: Multiple providers are available for runtime nativesdk-qemu (nativesdk-qemu, nativesdk-qemu-xilinx)
  Consider defining a PREFERRED_RPROVIDER entry to match nativesdk-qemu
  NOTE: Multiple providers are available for qemu-system-native (qemu-system-native, qemu-xilinx-system-native)
  Consider defining a PREFERRED_PROVIDER entry to match qemu-system-native

Signed-off-by: Niko Mauno <niko.mauno@vaisala.com>

meta-xilinx-core/conf/layer.conf

@@ -58,3 +58,9 @@ PREFERRED_VERSION_arm-trusted-firmware ?= "2.6-xilinx-${XILINX_RELEASE_VERSION}%
 PREFERRED_VERSION_u-boot-xlnx ?= "v2021.01-xilinx-${XILINX_RELEASE_VERSION}%"
 PREFERRED_VERSION_pmu-rom-native ?= "${@d.getVar("XILINX_RELEASE_VERSION").replace('v','')}"
 PREFERRED_VERSION_linux-xlnx ?= "${@'5.15.19' if d.getVar("XILINX_RELEASE_VERSION") == 'v2022.1' else '5.15.36'}%"
+
+# Weak defaults to avoid seeing redundant multiple provider notices
+PREFERRED_PROVIDER_nativesdk-qemu ??= "nativesdk-qemu"
+PREFERRED_PROVIDER_qemu-helper-native ??= "qemu-helper-native"
+PREFERRED_PROVIDER_qemu-native ??= "qemu-native"
+PREFERRED_PROVIDER_qemu-system-native ??= "qemu-system-native"