gitignore: ignore *.d files
gitignore: ignore *.d files

Makefile in trezor/trezor-mcu uses dependency generation now, without
ignoring these files, git marks the submodules as dirty.

trezor/trezor-qrenc,trezor/trezor-qrenc,BWallet/bwallet-qrenc,BWallet/bwallet-qrenc