V4L/DVB (9758): em28xx: replace some magic by register descriptions where known

Replaces all occurrences of em28xx_write_regs_req() and em28xx_write_reg()
used to setup register names by em28xx_write_reg().

Also, documents the register names that are known.

This patch were generated by this small perl script:

my %reg_map = (
	# Register table - the same as defined on parse_em28xx.pl script
);

while (<>) {
	if (m/(.*)em28xx_write_regs_req\(dev\,\s*0x00\,\s*(.*)\,\s*\"\\x(..)\",\s*1\)\;(.*)/) {
		my $reg = $2;
		my $val = $3;
		$val =~ tr/A-f/a-f/;
		$reg = $reg_map{$reg} if defined($reg_map{$reg});
		printf "$1em28xx_write_reg(dev, %s, 0x%s);$4\n", $reg, $val;
	} elsif (m/(.*)em28xx_write_regs\(dev\,\s*(.*)\,\s*\"\\x(..)\",\s*1\)\;(.*)/) {
		my $reg = $2;
		my $val = $3;
		$val =~ tr/A-f/a-f/;
		$reg = $reg_map{$reg} if defined($reg_map{$reg});
		printf "$1em28xx_write_reg(dev, %s, 0x%s);$4\n", $reg, $val;
	} else {
		print $_;
	}
}

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>