Add a new config option to allow to select the default compile
optimization level for the kernel.
Select the optimization for size by default if the small_flash feature is
set. Otherwise "Optimize for performance" is set.
Add the small_flash feature flag to all (sub)targets which had the
optimization for size in their default kernel config.
Remove CC_OPTIMIZE_FOR_* symbols from all kernel configs to apply the new
setting.
Exceptions to the above are:
- lantiq, where the optimization for size is only required for the
xway_legacy subtarget but was set for the whole target
- mediatek, ramips/mt7620 & ramips/mt76x8 where boards should have
plenty of space and an optimization for size doesn't make much sense
- rb532, which has 128MByte flash
Signed-off-by: Mathias Kresin <dev@kresin.me>
