[media] DocBook: upgrade media_api DocBook version to 4.2

Fixes the last three errors of media_api DocBook validatation:
(...)
media_api.xml:414: element imagedata: validity error : Value "SVG" for attribute format of imagedata is not among the enumerated set
media_api.xml:432: element imagedata: validity error : Value "SVG" for attribute format of imagedata is not among the enumerated set
media_api.xml:452: element imagedata: validity error : Value "SVG" for attribute format of imagedata is not among the enumerated set
(...)

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>