tools: move kermit files to tools/kermit directory

The script files, define2mk.sed and make-asm-offsets
are used to create autoconf.mk and asm-offsets.h
while build.

Whereas README, dot.kermrc, flash_param, send_cmd, send_image
are files useful for kermit.

We should not put files which have the totally different purpose
into the same directory.

This commit creates a new directory, tools/kermit,
and move kermit files into it.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Wolfgang Denk <wd@denx.de>