tools: convert makefiles to kbuild style

Before this commit, makefiles under tools/ directory
were implemented with their own way.

This commit refactors them by using "hostprogs-y" variable.

Several C sources have been added to wrap other C sources
to simplify Makefile.
For example, tools/crc32.c includes lib/crc32.c

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

tools/.gitignore

@@ -6,6 +6,7 @@
 /dumpimage
 /mkenvimage
 /mkimage
+/mkexynosspl
 /mpc86x_clk
 /mxsboot
 /ncb
@@ -15,7 +16,6 @@
 /xway-swap-bytes
 /*.exe
 /easylogo/easylogo
-/env/crc32.c
 /env/fw_printenv
 /gdb/gdbcont
 /gdb/gdbsend