gpio/basic_mmio: add missing include of spinlock_types.h

include/linux/basic_mmio_gpio.h uses a spinlock_t without including any
of the spinlock headers resulting in this compiler warning.

include/linux/basic_mmio_gpio.h:51:2: error: expected specifier-qualifier-list before 'spinlock_t'

Explicitly include linux/spinlock_types.h to fix it.

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>