Remove residual blank line at start of Makefile

This is a residual of the $FreeBSD$ removal.

MFC After: 3 days (though I'll just run the command on the branches)
Sponsored by: Netflix

Remove $FreeBSD$: one-line sh pattern

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

Make basic Broadcom I/O space reading functions work

It's now possible to use Broadcom functions to read the I/O registers of
SDIO card. The functions were copied from the BSD-licensed Broadcom Linu

Make basic Broadcom I/O space reading functions work

It's now possible to use Broadcom functions to read the I/O registers of
SDIO card. The functions were copied from the BSD-licensed Broadcom Linux driver
as-is. To make it possible, a small Linux compatibility layer was introduced.

Currently the card responds with the correct version number ("magic")
when reading the corresponding address.

Approved by: imp (mentor)
Differential Revision: https://reviews.freebsd.org/D12111

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Added new tool for doing experiments with SDIO card.

Due to its experimental nature, it's not yet connected to the build.

Submitted by: Ilya Babulin