arm: Make sure we can handle a thumb entry point.

Similarly to what's been done on arm64 with commit
712c060c94, when executing a binary, if the
entry point is a thumb symbol, then make sure we set the PSL_T flag, otherwise
the CPU will interpret it in ARM mode, and that will likely leads to an
undefined instruction.

PR:	256899
MFC after: 	1 week

sys/arm/arm/machdep.c

@@ -346,6 +346,8 @@ exec_setregs(struct thread *td, struct image_params *imgp, uintptr_t stack)
 	tf->tf_svc_lr = 0x77777777;
 	tf->tf_pc = imgp->entry_addr;
 	tf->tf_spsr = PSR_USR32_MODE;
+	if ((register_t)imgp->entry_addr & 1)
+		tf->tf_spsr |= PSR_T;
 }
 
 #ifdef VFP