ARM: 8124/1: don't enter kgdb when userspace executes a kgdb break instruction

ARM: 8124/1: don't enter kgdb when userspace executes a kgdb break instruction

The kgdb breakpoint hooks (kgdb_brk_fn and kgdb_compiled_brk_fn)
should only be entered when a kgdb break instruction is executed
from the kernel. Otherwise, if kgdb is enabled, a userspace program
can cause the kernel to drop into the debugger by executing either
KGDB_BREAKINST or KGDB_COMPILED_BREAK.

Acked-by: Will Deacon <[email protected]>
Signed-off-by: Omar Sandoval <[email protected]>
Signed-off-by: Russell King <[email protected]>