ANDROID: GKI: enable CONFIG_USB_ROLE_SWITCH

It's already enabled in arm64 gki_defconfig by virtue of other
dependancies dragging it in, but enable it in x86 gki_defconfig to
provide good code coverage.

Bug: 163379072
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I26707e49046888e9d4b607e4b6d7766610cedfa1