readelf: Handle 0 sh_entsize of GOT sections

Gold, lld and mold set sh_entsize to 0 on .got and .got.plt sections.
If sh_entsize of GOT sections is 0, assume 8 for ELFCLASS64 and 4 for
ELFCLASS32, except for x32 which uses 8.

	PR binutils/33368
	* readelf.c (process_got_section_contents): Handle 0 sh_entsize
	of GOT sections.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>