[.gitignore] please add generated file to .gitignore

[Kevin Du Huanpeng]

Hi, is anyone know the these two files used for:
	scripts/fix_size
	scripts/kernel-install
it seem generated and it's a binary executable file , if so please add it to
.gitignore
1. git clone ....
2. set ARCH & CROSS_COMPILE
3.  make qemu-malta_defconfig
4. make 
5. git status
dev at bogon:~/barebox$ git status
# On branch master
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#       scripts/fix_size
#       scripts/kernel-install