frdm_k64f: hexiwear_k64: Fix accel interrupt pinmux settings

The k64 gpio driver quietly initializes the pinmux to force the pin to
be a gpio, regardless of the setting defined by the board's pinmux
table, or even if the pin was not in the pinmux table.

This behavior caused the accelerometer interrupt pin to be incorrectly
defined in the frdm_k64f and hexiwear_k64 pinmux tables.

Change-Id: If46df0e051452fef291d5ad5cdff56463d5f465e
Signed-off-by: Maureen Helm <maureen.helm@nxp.com>