.gitignore: Split into subdirectory files

There's no need for the global list of files to ignore, so use git's
ability to work with more local configuration.

Change-Id: I50882e6756cbc0fdfd899353cc23962544690fb3
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46879
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Christian Walter <christian.walter@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/crossgcc/.gitignore

@@ -0,0 +1,28 @@
+acpica-unix-*/
+binutils-*/
+build-*BINUTILS/
+build-*EXPAT/
+build-*GCC/
+build-*GDB/
+build-*GMP/
+build-*LIBELF/
+build-*MPC/
+build-*MPFR/
+build-*PYTHON/
+build-*LVM/
+build-*IASL/
+expat-*/
+gcc-*/
+gdb-*/
+gmp-*/
+libelf-*/
+mingwrt-*/
+mpc-*/
+mpfr-*/
+Python-*/
+*.src/
+tarballs/
+w32api-*/
+xgcc/
+xgcc-*/
+xgcc