Revert configurations for UVISOR_DISABLED (from v2.1.0)

This patch reverts the previous release. No functionality is changed with respect to that, but a bug in the way disabled.c handles interrupts is temporarily fixed.

A better fix will be provided with a later release.

Bug fixes

• [workaround] Applications running with UVISOR_SUPPORTED and UVISOR_DISABLED were hanging in an interrupt handler.

Update uvisor-lib build system

The new build system provides more support for unsupported/uVisor-disabled platforms.

• ARMmbed/uvisor is fetched as a sub-module.
• The release libraries are fetched directly from the submodule.
• Unsupported platforms only add unsupported.c as a source file to be compiled by yotta.
• Disabled platforms still link uVisor but with UVISOR_DISABLED set.

Box identity and EFM32 support

Breaking APIs

• Applications using UVISOR_BOX_CONFIG(...) will not work after this update if they do not include a call to the UVISOR_BOX_NAMESPACE(...) as well.
• All other APIs are backwards compatible. This update only affects applications actively using uVisor, not yotta modules depending on it.

New features

• APIs for box identity. See the updated documentation.

New platforms

• Now supporting the whole Cortex-M3 and Cortex-M4 based EFM32 family from Silicon Labs.

For more details checkout the release notes of the corresponding ARMmbed/uvisor@54fe069 release.