multimedia/x265: fix HDR10+ support

Currently, the FreeBSD build of multimedia/x265 fails to include HDR10+
(a.k.a. HDR10plus or "dynamic HDR") support. It only includes HDR10
support (without "plus", sometimes referred to as "static HDR").
That problem also affects the ffmpeg port because it uses the x265 port
for encoding. And that, in turn, affects many other ports that use
ffmpeg or its library for encoding. In other words, the problem renders
several ports unable to produce HDR10+ video content.

There is a non-default cmake build option ENABLE_HDR10_PLUS, but the
port does not handle it correctly.

PR: 280208
Approved by: Mikhail T. <freebsd-2024@virtual-estates.net> (maintainer)