tools/mtd-utils: Mark some lzma functions as static

tools/mtd-utils: Mark some lzma functions as static

These functions are not declared in any header file and only used in
same compile unit, mark them as static to remove one gcc warning and
make it easier for the compiler to optimize them out.

This also fixes some style problems to make this patch match the version
in the packages folder.

This is copied from this commit to the mtd-utils we pack into the image:
56d0dd56e9c6efa79 ("mtd-utils: Mark some lzma functions as static")

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Tested-by: Koen Vandeputte <koen.vandeputte@ncentric.com>