spi: gpio: Support a single always-selected device

spi: gpio: Support a single always-selected device

The generic SPI code, the SPI GPIO driver functions support
a single always-connected device cases. The only impediment
is that board instantiation prevents that from happening.
Update spi_gpio_probe_pdata() checks to support the mentioned
hardware setup.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20250205132127.742750-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>