rimage: add missing include for Panther Lake platform

This patch adds the missing include for the Panther Lake (PTL) platform
in the rimage configuration file. The absence of this include was
causing issues with signing the LLEXT RTC library during CI builds.

Changes include:
- Adding the include directive for the Panther Lake platform in the
  tools/rimage/config/platform.toml file.

This change ensures that the rimage tool correctly processes the
configuration for the Panther Lake platform, resolving the issue with
signing the LLEXT RTC library.

Signed-off-by: Tomasz Leman <tomasz.m.leman@intel.com>

Author: tmleman

tools/rimage/config/platform.toml

@@ -2,4 +2,6 @@
 #include "platform-mtl.toml"
 #elif CONFIG_LUNARLAKE
 #include "platform-lnl.toml"
+#elif CONFIG_PANTHERLAKE
+#include "platform-ptl.toml"
 #endif