usb: ehci: Add support for SINGLE_STEP_SET_FEATURE test of EHSET

Embedded High-speed Host Electrical Test or EHSET defines following
tests for a USB Host port:
1: TEST_SE0
2: TEST_J
3: TEST_K
4: TEST_PACKET
5: HS_HOST_PORT_SUSPEND_RESUME
6: SINGLE_STEP_GET_DEV_DESC
7: SINGLE_STEP_SET_FEATURE

Tests 1-4 needs support from EHCI i.e setting test control bits in
PORTSC register.
Tests 5&6 dont require any additional support from EHCI stack.
Where as 7th test requires support in EHCI and is being added in this
patch.

For SINGLE_STEP_SET_FEATURE test, first the SETUP request of GetDesc
is sent which is followed by the IN stage after a delay of 15 secs.

SINGLE_STEP_SET_FEATURE test can be initiated like any other 1-4 Test
by issuing a SetFeature request to the root hub with Test-Selector
value = 0x06.

Change-Id: I6ad2bd5fc14c31c80f0291a82fef40c2c5a9045a
Signed-off-by: Manu Gautam <mgautam@qualcomm.com>