build(core): do not propagate PYOPT to kernel build to work around a …

…build error

the error:

When built with PYOPT, Optiga will log its communication to the VCP. But
now that VCP config lives in coreapp and Optiga lives in kernel, there's
no way for Optiga to write to VCP, and the relevant calls simply don't
build.

We need a different method for logging inside the kernel.

core/Makefile

@@ -300,7 +300,7 @@ build_reflash: ## build reflash firmware + reflash image
 	dd if=build/bootloader/bootloader.bin of=$(REFLASH_BUILD_DIR)/sdimage.bin bs=1 seek=49152
 
 build_kernel: ## build kernel image
-	$(SCONS) $(KERNEL_BUILD_DIR)/kernel.bin
+	$(SCONS) PYOPT=1 $(KERNEL_BUILD_DIR)/kernel.bin
 
 build_firmware: templates build_cross build_kernel ## build firmware with frozen modules
 	$(SCONS) $(FIRMWARE_BUILD_DIR)/firmware.bin