Update mach-hkdk4412.c

This patch adds support for 1-wire bus on pin 6 of the U3 I/O header. To use it CONFIG_W1_MASTER_GPIO must be enabled in kernel config. Enabling W1 breaks support for the U3 I/O shield board.
Merge pull request #38 from Reichl/odroid-3.8.y

Update mach-hkdk4412.c