x86/traps: widen condition for logging top-of-stack

x86/traps: widen condition for logging top-of-stack

Despite -fno-omit-frame-pointer the compiler may omit the frame pointer,
often for relatively simple leaf functions. (To give a specific example,
the case I've run into this with is _pci_hide_device() and gcc 8.
Interestingly the even more simple neighboring iommu_has_feature() does
get a frame pointer set up, around just a single instruction. But this
may be a result of the size-of-asm() effects discussed elsewhere.)

Log the top-of-stack value if it looks valid _or_ if RIP looks invalid.

Also annotate all stack trace entries with a marker, to indicate their
origin:
R: register state
F: frame pointer based
S: raw stack contents

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>