gdb: mips: Fix large-frame.exp test case failure

gdb: mips: Fix large-frame.exp test case failure

$ objdump -d outputs/gdb.base/large-frame/large-frame-O2
0000000120000b20 <func>:
   120000b20:   67bdbff0        daddiu  sp,sp,-16400
   120000b24:   ffbc4000        sd      gp,16384(sp)
   120000b28:   3c1c0002        lui     gp,0x2
   120000b2c:   679c8210        daddiu  gp,gp,-32240
   120000b30:   0399e02d        daddu   gp,gp,t9
   120000b34:   df998058        ld      t9,-32680(gp)
   120000b38:   ffbf4008        sd      ra,16392(sp)
   120000b3c:   0411ffd8        bal     120000aa0 <blah>
...

The disassembly of the above func function shows that we may use
instructions such as daddiu/daddu, so add "daddiu $gp,$gp,n",
"daddu $gp,$gp,$t9" and "daddu $gp,$t9,$gp" to the mips32_scan_prologue
function to fix the large-frame.exp test case.

Before applying the patch:

 backtrace
 #0  blah (a=0xfffffee220) at .../gdb/testsuite/gdb.base/large-frame-1.c:24
 #1  0x0000000120000b44 in func ()
 Backtrace stopped: frame did not save the PC
 (gdb) FAIL: gdb.base/large-frame.exp: optimize=-O2: backtrace

 # of expected passes            5
 # of unexpected failures        1

After applying the patch:

 # of expected passes            6

Signed-off-by: Youling Tang <tangyouling@loongson.cn>