Update `x11/nvidia-driver' to version 390.87, which fixed a resource
leak introduced in the 390 series of drivers that could lead to reduced
performance after starting and stopping several OpenGL and/or Vulkan
applications. While here, replace deprecated @[un]exec keywords which
do not specify when they should be executed with @post[un]exec and move
KPI-related patching to a better place within the Makefile.

PR: 231721