arm64/rockchip: Fix the build with GCC

We were missing brackets in GPIO_FLAGS_PINCTRL. Without them GCC
complains a use is ambiguous. Fix by adding the needed brackets.

Reviewed by: manu, brooks, imp, jhb, emaste
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D45264

(cherry picked from commit 4f012d7a7a473d2486f01ce355fd2c79c3d43db6)