LD/testsuite: Fix undefined symbol tests for MIPS and S+core targets

Fix commit 647d4de92e06 ("Test undefined symbols in shared libraries")
and remove "undefined symbols in shared lib (dyn reloc)" test failures
for MIPS and S+core targets.

This test assumes 3 dynamic relocation entries, however the respective
psABIs define an extra single dummy *_NONE relocation at the beginning
of the dynamic relocation table, which results in test output like the
following for MIPS:

Relocation section '.rel.dyn' at offset 0x33c contains 4 entries:
 Offset     Info    Type            Sym.Value  Sym. Name
00000000  00000000 R_MIPS_NONE
00010364  00000903 R_MIPS_REL32      00000000   undef_pfun
00010360  00000a03 R_MIPS_REL32      00000000   undef_data
00010368  00000b03 R_MIPS_REL32      00000000   undef_notype

and S+core:

Relocation section '.rel.dyn' at offset 0x274 contains 4 entries:
 Offset     Info    Type            Sym.Value  Sym. Name
00000000  00000000 R_SCORE_NONE
5ffe0464  00000e12 R_SCORE_REL32     00000000   undef_notype
5ffe045c  00000f12 R_SCORE_REL32     00000000   undef_data
5ffe0460  00001012 R_SCORE_REL32     00000000   undef_pfun

targets respectively, and also n64 MIPS targets pad relocation triplets
they use with extra *_NONE relocations, resulting in output like this:

Relocation section '.rel.dyn' at offset 0x4c0 contains 4 entries:
  Offset          Info           Type           Sym. Value    Sym. Name
000000000000  000000000000 R_MIPS_NONE
                    Type2: R_MIPS_NONE
                    Type3: R_MIPS_NONE
000000010508  000900001203 R_MIPS_REL32      0000000000000000 undef_pfun
                    Type2: R_MIPS_64
                    Type3: R_MIPS_NONE
000000010500  000a00001203 R_MIPS_REL32      0000000000000000 undef_data
                    Type2: R_MIPS_64
                    Type3: R_MIPS_NONE
000000010510  000b00001203 R_MIPS_REL32      0000000000000000 undef_notype
                    Type2: R_MIPS_64
                    Type3: R_MIPS_NONE

Expect the right number of *_NONE relocations then, and adjust the total
number of relocations expected accordingly.

	ld/
	* testsuite/ld-undefined/undefined.exp: Correct the dyn reloc
	test for MIPS and S+core targets.