usb: gadget: f_fs: Add flags to descriptors block

usb: gadget: f_fs: Add flags to descriptors block

This reworks the way SuperSpeed descriptors are added and instead of
having a magic after full and high speed descriptors, it reworks the
whole descriptors block to include a flags field which lists which
descriptors are present and makes future extensions possible.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
[backport from upstream commit 410b1f0e1c86443c57dc70d78db7aec193c79787]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-id: I410b1f0e1c86443c57dc70d78db7aec193c79787