remoteproc: elf_loader: skip segment with memsz as zero

remoteproc: elf_loader: skip segment with memsz as zero

Per elf specification,
p_filesz: This member gives the number of bytes in the file image of
the segment; it may be zero.
p_memsz: This member gives the number of bytes in the memory image
of the segment; it may be zero.

There is a case that i.MX DSP firmware has segment with PT_LOAD and
p_memsz/p_filesz set to zero. Such segment needs to be ignored,
otherwize rproc_da_to_va would report error.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20220413033038.1715945-2-peng.fan@oss.nxp.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>