usb: gadget: Drop all gadget_is_*() functions

usb: gadget: Drop all gadget_is_*() functions

The only actually used gadget_is_*() functions are the one for DWC3
used in epautoconf.c usb_ep_autoconfig() and one for MUSB in ether.c.
The DWC3 one should be fixed in some separate patch.

Inline the gadget_is_dwc3() and stop using ifdefs in favor of
IS_ENABLED() macro.

The rest of gadget_is_*() calls in usb_ep_autoconfig() can never
be anything but 0, since those gadgets are not supported in U-Boot,
so remove all that unused code. Remove gadget_chips.h as well.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Tested-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # on vim3
Link: https://lore.kernel.org/r/20240609213449.194762-4-marek.vasut+renesas@mailbox.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>