Fix regression on s390x with entry-values.exp.

Fix regression on s390x with entry-values.exp.

The trace-specific test case 'entry-values' concludes fairly late in
the process that this platform doesn't support trace.  Before that,
there are some platform specifics that don't work on s390x.  The fix
addresses two aspects:

(1) Removal of an excess space character in the regex for the
    disassembly.  This is needed when there is a function alignment
    gap, because then the hex address is immediately followed by a
    colon, like in the first 'nopr' line below:

    (gdb) disassemble foo+50,+10
    Dump of assembler code from 0x32 to 0x3c:
       0x0000000000000032 <foo+50>: br      %r4
       0x0000000000000034:  nopr    %r7
       0x0000000000000036:  nopr    %r7
       0x0000000000000038 <bar+0>:  stmg    %r11,%r15,88(%r15)
    End of assembler dump.

(2) Handling for the s390-specific call instruction.

gdb/testsuite/ChangeLog:
	* gdb.trace/entry-values.exp: Remove excess space character from
	regex patterns.  Handle s390 call instruction.