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.
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