tests: drivers: sensor: spi: include `gpio.h` header

This patch adds a missing include directive to `spi.dtsi` in the
`build_all` configuration.The include is required because commit
2ac31646 introduced the use of `GPIO_ACTIVE_HIGH` and `GPIO_ACTIVE_LOW`
macros.

Signed-off-by: Patryk Koscik <pkoscik@antmicro.com>