Refactor gcc arm exporter templates

[chrta]

All gcc arm exporter templates are changed, but EFM32 ones. They have another internal structure and can be adapted later on.

The main logic is now in the file workspace_tools/export/gcc_arm_common.tmpl
All target platforms now support the same make targets with the same behavior.

Main changes:

• All Cortex M0(+) targets exclude the floating point support for printf and scanf, see https://github.com/mbedmicro/mbed/compare/mbedmicro:master...chrta:refactor_gcc_arm_exporter_templates?expand=1#diff-8d651adf7eb70cde396310b384cf3e5fR42 and the following line.
• All Cortex M4F-Cores now support setting the float-abi via make parameter.
• The cpu compiler flags are now taken from the toolchain class and used in the templates

This relates to #370

[0xc0170]

Hi,

thanks for this refactoring, I glanced over the files, need to pull it to tests and review further

[0xc0170]

I exported couple of projects for some boards, did not have any problems.

Can you please rebase to the latest master ? I merged this locally, did not see any conflicts, but github says there are. Let me know.

[chrta]

I merged the current master in without any conflicts. Or should i rework the branch and do a rebase?

[0xc0170]

rebase would be optimal, but not required.

[chrta]

Rebased

[0xc0170]

Thanks !