clang-format: Update .clang-format to be compliant with linux kernel coding style

* The coreboot clang format file seems to be incomplete.
* Add missing options.

Change-Id: I61a32ed951d18d5865be201bb38d18e50dd76f08
Signed-off-by: Philipp Deppenwiese <zaolin@das-labor.org>
Reviewed-on: https://review.coreboot.org/25687
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

.clang-format

@@ -1,6 +1,10 @@
-BasedOnStyle: LLVM
-IndentWidth: 8
-UseTab: Always
-BreakBeforeBraces: Linux
-AllowShortIfStatementsOnASingleLine: false
-IndentCaseLabels: false
+BasedOnStyle:                              LLVM
+Language:                                  Cpp
+IndentWidth:                               8
+UseTab:                                    Always
+BreakBeforeBraces:                         Linux
+AllowShortIfStatementsOnASingleLine:       false
+IndentCaseLabels:                          false
+SortIncludes:                              false
+ContinuationIndentWidth:                   8
+ColumnLimit:                               80