gdb.trace/testsuite: Bump stack collection fudge factor.

gdb.trace/testsuite: Bump stack collection fudge factor.

These two tests collect 64 words from $sp onwards, hoping that's enough
to capture a few whole stack frames.  Unfortunately, that's not enough
for s390, which tends to have large frame sizes - minimum 24 words on
s390, 20 on s390x (which just barely passes).  Bump it to 128 words,
let's hope no machine needs more.

Tested on x86_64, s390, s390x.

gdb/testsuite/ChangeLog:

	* gdb.trace/backtrace.exp: Bump stack collection fudge factor.
	* gdb.trace/entry-values.exp: Bump stack collection fudge factor.