libdwfl: elf_from_remote_memory should use pagesize, not p_align.

libdwfl: elf_from_remote_memory should use pagesize, not p_align.

elf_from_remote_memory would use the actual p_align of the PT_LOAD segments
to calculate the loadbase, end and start of a segment. But the dynamic
loader aligns the segments using the pagesize and only sanity checks the
p_align values. So we should do the same to get accurate segment addresses.
Also fixes a small memory leak in case the ELF image appears to be bad.

Signed-off-by: Mark Wielaard <mjw@redhat.com>