openrisc: traps: Don't send signals to kernel mode threads

In the Linux kernel, the following vulnerability has been resolved: openrisc: traps: Don't send signals to kernel mode threads OpenRISC exception handling sends signals to user processes on floating point exceptions and trap instructions (for debugging) among others. There is a bug where the trap handling logic may send signals to kernel threads, we should not send these signals to kernel threads, if that happens we treat it as an error. This patch adds conditions to die if the kernel receives these exceptions in kernel mode code.