Bring a few simplifications to a10_gpio:

o Return the real hardware state in gpio_pin_getflags() instead of keep

the last state in an internal table.  Now the driver returns the real
state of pins (input/output and pull-up/pull-down) at all times.

o Use a spin mutex. This is required by interrupts and the 1-wire code.
o Use better variable names and place parentheses around them in MACROS.
o Do not lock the driver when returning static data.

Tested with gpioled(4) and DS1820 (1-wire) sensors on banana pi.