ld: Update PR ld/25237 test

1. Skip targets which don't support the .bss section alignment, 1 << 16.
2. Replace .bss with ".section .bss".
3. Use ".zero 0xb60000" for targets which pad the section to its alignment.

	PR ld/25237
	* testsuite/ld-elf/pr25237.d: Skip avr-*-* and h8300-*-*.
	Update expected segment size to 0xb60000.
	* testsuite/ld-elf/pr25237.s: Use ".section .bss" and
	".zero 0xb60000".

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