fastboot: Fix wMaxPacketSize for High-Speed IN endpoint

wMaxPacketSize for IN endpoing in High-Speed must be 512 and not 64.
While fixing that we do some clean ups like

- use cpu_to_le16(decimal_length) instead of hexadecimal length.
- No need to initialize bInterval to 0. Static variables are 0 initialized.
- Move descriptor setting from fastboot_add to to fastboot_bind.
- check for dual speed configuration before setting the high speed descriptors.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Tested-by: Steve Rae <srae@broadcom.com>
Tested-by: Steve Rae <srae@broadcom.com> [Test HW: bcm235xx board]