sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

sys/modules: normalize .CURDIR-relative paths to SRCTOP

This simplifies make output/logic

Tested with: `cd sys/modules; make ALL_MODULES=` on amd64
MFC after: 1 month
Sponsored by: Dell EMC Isilon

add a module that provides support for DRAM ECC error injection on AMD CPUs

I imagine that the module would be useful only to a very limited number
of developers, so that's my excuse for not writing any documentation.
On a more serious note, please see DRAM Error Injection section of BKDGs
for families 10h - 16h. E.g. section 2.13.3.1 of BKDG for AMD Family 15h
Models 00h-0Fh Processors.

Many thanks to kib for his suggestions and comments.

Discussed with: kib
MFC after: 3 weeks
Differential Revision: https://reviews.freebsd.org/D9824