u-boot: Move allwinner 64 bits dep to u-boot-master

We have more than one Allwinner 64bits SoC u-boot ports now
and others are coming.
Move the dependencies into the u-boot-master ports.

While here, switch maintainer on u-boot-pine64 and u-boot-sopine
to uboot@ as discussed with imp@ and brd@

Reviewed by: imp (maintainer)
Approved by: imp
Differential Revision: https://reviews.freebsd.org/D13450