movdec: handle 0x7fff langcode as macintosh per the specs

The correct point that seperates ISO and MAC language codes is 0x400
according to the current QT spec. Old QT specs did not list where this
seperation is but apparently only defined the meaning of the first 137.

(cherry picked from commit 9e71cc81f3655cacf0f91860fba3043f13b64059)
(cherry picked from commit 7940306a47df602be4f57a62175706265bbfd0aa)
isom: lpcm in mov default to big endian

It is my understanding that "Unless otherwise stated, all data in a
QuickTime movie is stored in big-endian byte ordering" [1] in MOV files.

I have a couple of thousand files, which technically are invalid because
their sound sample description element 4CC is 'lpcm' but its version is
0 - and "Version 0 supports only uncompressed audio in raw ('raw ') or
twos-complement ('twos') format" [2]

Because isom.c only contains a mapping for 4CC 'lpcm' to
AV_CODEC_ID_PCM_S16LE, these files have their audio decoded as LE when
it is actually BE.

This commit adds AV_CODEC_ID_PCM_S16BE as the first match for 4CC 'lpcm'.

[1]
https://developer.apple.com/library/mac/documentation/quicktime/QTFF/qtff.pdf
page 21
[2]
https://developer.apple.com/library/mac/documentation/quicktime/QTFF/qtff.pdf
page 178

Reviewed-by: Yusuke Nakamura <muken.the.vfrmaniac@gmail.com>