Add support for vApplicationFPUSafeIRQHandler (#1113)

Add support for vApplicationFPUSafeIRQHandler (#1113)

This PR adds support for vApplicationFPUSafeIRQHandler. The application
writer needs to name their IRQ handler as:
1. vApplicationIRQHandler if the IRQ handler does not use FPU registers.
2. vApplicationFPUSafeIRQHandler is the IRQ handler uses FPU registers.

When the application uses vApplicationFPUSafeIRQHandler, a default
implementation of vApplicationIRQHandler is used which stores FPU
registers and then calls vApplicationFPUSafeIRQHandler.