sysutils/cpu-microcode-intel: Dont depend on cpu-microcode-rc

All Intel systems running 15.0 or 14.3 support loading at boot time
without cpu-microcode-rc, therefore, do not depend on it by default.
Update the package message with the current up-to-date instructions.

Approved by: jrm (maintainer)
Differential Revision: https://reviews.freebsd.org/D54515