kdb: Remove stack dump when entering kgdb due to NMI

Issuing a stack dump feels ergonomically wrong when entering due to NMI.

Entering due to NMI is normally a reaction to a user request, either the
NMI button on a server or a "magic knock" on a UART. Therefore the
backtrace behaviour on entry due to NMI should be like SysRq-g (no stack
dump) rather than like oops.

Note also that the stack dump does not offer any information that
cannot be trivial retrieved using the 'bt' command.
Signed-off-by: NDaniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: NJason Wessel <jason.wessel@windriver.com>

kernel/debug/kdb/kdb_main.c

@@ -1247,7 +1247,6 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs,
 		kdb_printf("due to NonMaskable Interrupt @ "
 			   kdb_machreg_fmt "\n",
 			   instruction_pointer(regs));
-		kdb_dumpregs(regs);
 		break;
 	case KDB_REASON_SSTEP:
 	case KDB_REASON_BREAK: