V4L/DVB (8092): videodev: simplify and fix standard enumeration

VIDIOC_ENUMSTD did not return all the PAL/SECAM/NTSC variants: it just returned
one single PAL/SECAM/NTSC standard without separate entries for the trickier
standards like NTSC-JP.

Changed the code so that it behaves better.

Also simplified the if/switch statements into a common standards lookup table.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>