arch/arm64/armv8: Add exception output without printk

In case printk does not work the current exception handler will print a
simple "!" to notify the developer that coreboot is actually there but
something went wrong.

The "!" can be quite confusing when it actually happens that printk does
not work. Since "!" doesn't really say much (if you don't know the
exception arm64 code) the developer (like me) can easily assume that
something went wrong while configuring clocks or baud rate of UART,
since the output seemingly does not seem to make sense.

This adds a little bit more output to assure the developer that what was
printed was actually intended to be printed. Therefore it prints "FAIL"
which assures the developer that this was intended output. It also adds
a comment above so that developer can more easily grep for this message.

Signed-off-by: Maximilian Brune <maximilian.brune@9elements.com>
Change-Id: I2f858730469fff3cae120fd7c32fec53b3d309ca
---
M src/arch/arm64/armv8/exception.c
M src/arch/arm64/include/armv8/arch/exception.h
2 files changed, 30 insertions(+), 1 deletion(-)