linux-user: Honor elf alignment when placing images

linux-user: Honor elf alignment when placing images

Most binaries don't actually depend on more than page alignment,
but any binary can request it.  Not honoring this was a bug.

This became obvious when gdb reported

    Failed to read a valid object file image from memory

when examining some vdso which are marked as needing more
than page alignment.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit c81d1fafa6233448bcc2d8fcd2ba63a4ae834f3a)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>