The GCC Optimization Levels AGAIN [2/2]

So after lurking around, I found out that we didn't set up the GCC Optimization
Levels to the TARGET_linux_mips.mk and I also found out that the Global Cflags
for TARGET_linux-x86.mk uses O2 in by default. Now I added those GCC
Optimization Levels to it but I'm not sure if they work? ¯\_(ツ)_/¯

PS2: Rebase.
PS3: Update the commit message.

Change-Id: I89ca753723fbbc69d2fe07fec4b3f5f756d42ecc
Signed-off-by: Lokesh Chamane <lokesh.c703@gmail.com>