spi:sunxi: spi board IRQ setting with GPIO management

Read "irq_gpio" value from script.bin and use it to set the IRQ for the SPI board. Some SPI boards should need a IRQ to work properly and register the irq handler inside the device driver.
The "irq_gpio" value is converted using gpiolib function "gpio_to_irq" and assigned to the specific board irq field.

Here is an example of script.txt configuration:

[spi_board0]
modalias = "sun5i_enc28j60"
max_speed_hz = 10000000
chip_select = 0
bus_num = 2
mode = 0
irq_gpio = 1

[gpio_para]
gpio_used = 1
gpio_num = 1
gpio_pin_1 = port:PB04<6><default><default><default>

In this case you can easily assign the PB04 corrensponding interrupt to the network device using the virtual IRQ created by the GPIOlib.

Signed-off-by: Lorenzo Nava <lorenx4@gmail.com>

v3 => v4: Fix gpio_request and spi message

v2 => v3: Fix indentations from hard tabs to spaces

v1 => v2: Fix driver failure when no irq definition was found in script.bin config file