Remove enforced compilation flags from CMake files

Hello,

Currently, a lot of compiler flags is forcefully set in
media_driver/cmake/linux/media_compile_flags_linux.cmake

This makes packaging driver by distributions complicated, as compilation flags (-march, -mtune, etc) should be passed from distribution rules (RPM specs, debian/rules, Gentoo ebuilds/make.conf, etc.).

Please, remove most of them.