All driver APIs (i2c, spi, gpio, etc.) return 'int' type, but pinmux
APIs. So this patch changes the returning type from 'uint32_t' to
'int' from include/pinmux.h and fixes all pinmux drivers according.
Besides keeping consistency between all drivers APIs, this patch is
also applicable for the errno.h code transition. Pinmux drivers will
return negative errno.h codes so returning 'int' is more suitable
than 'uint32_t'.
Change-Id: I2a6e92d567a0e21fec363226da6197df94657d4b
Signed-off-by: Andre Guedes <andre.guedes@intel.com>