recipes-bsp/optee-ftpm: optee-ftpm package needs to be cross compiled

[rakeshk7097]

optee-ftpm builds successfully only in cross-compilation mode; therefore, setting the recipe to default to cross-compilation can resolve the following build error.

make[2]: Entering directory '/<<PKGBUILDDIR>>/Samples/ARM32-FirmwareTPM/optee_ta' /usr/bin/make -C fTPM CROSS_COMPILE= make[3]: Entering directory '/<<PKGBUILDDIR>>/Samples/ARM32-FirmwareTPM/optee_ta/fTPM' Checking symlink to the TPM folder: /<<PKGBUILDDIR>> Checking symlink to the WolfSSL folder: /<<PKGBUILDDIR>>/external/wolfssl Establishing symlink. Establishing symlink. CC ../out/fTPM/platform/AdminPPI.o CC ../out/fTPM/platform/Cancel.o make[3]: *** No rule to make target 'lib/wolf/wolf_symlink/wolfcrypt/src/aes.c', needed by '../out/fTPM/./lib/wolf/wolf_symlink/wolfcrypt/src/aes.o'. Stop. make[3]: *** Waiting for unfinished jobs.... CC ../out/fTPM/platform/Clock.o CC ../out/fTPM/platform/Entropy.o CC ../out/fTPM/platform/LocalityPlat.o CC ../out/fTPM/platform/NvAdmin.o CC ../out/fTPM/platform/NVMem.o CC ../out/fTPM/platform/PowerPlat.o CC ../out/fTPM/platform/PlatformData.o CC ../out/fTPM/platform/PPPlat.o CC ../out/fTPM/platform/RunCommand.o CC ../out/fTPM/platform/Unique.o CC ../out/fTPM/platform/EPS.o CC ../out/fTPM/platform/PlatformACT.o CC ../out/fTPM/reference/RuntimeSupport.o CC ../out/fTPM/platform/fTPM_helpers.o CC ../out/fTPM/fTPM.o make[3]: Leaving directory '/<<PKGBUILDDIR>>/Samples/ARM32-FirmwareTPM/optee_ta/fTPM' make[2]: *** [Makefile:6: all] Error 2