Improve consistency of indentation in Makefile

Only use one consecutive tab in make rules and use spaces
for any additional indentation. This should generally prevent
tabs from appearing on the cmdline.

This cl is the result of 3 regex replaces:
\\\n\t\t([^\t]) -> \\\n\t    \1
\\\n\t\t\t([^\t]) -> \\\n\t        \1
\\\n\t\t\t\t([^\t]) -> \\\n\t            \1

Test: make mainline_system_arm64
Change-Id: Ic3f72deed35e39e4b1a4b492db65aeabc5bef0d5