Changed console initialization

[bogdanm]

All the initialization related to console operations (stdout/stderr/stdin)
now happens in retarget.cpp. The relevant parts will be removed from the
target specific code in subsequent commits.

[bogdanm]

Also fixes #132
Tested on FRDM-K64F.

[bogdanm]

DO NOT MERGE without ARMmbed/mbed-hal-ksdk-mcu#54 and ARMmbed/mbed-hal-st-stm32f4#31

[bogdanm]

@0xc0170

[0xc0170]

Should stdio_uart_inited flag be set to 1 once initialized = stdio_uart only initialized once?

+1 I am trying to understand why HAL was setting init flag and copying the structure (I dont think we used that updated structure anywhere).

[bogdanm]

Should stdio_uart_inited flag be set to 1 once initialized = stdio_uart only initialized once?

Ah, of course, you're right. I'll fix that.

I am trying to understand why HAL was setting init flag and copying the structure (I dont think we used that updated structure anywhere).

I'm trying to understand why we did stdio initialization in the HALs at all. If we had a reason, I don't remember it.

[0xc0170]

I added the same changeset to nrf51822: ARMmbed/mbed-hal-nrf51822-mcu#39

[bogdanm]

Fixed initialization sequence.

[0xc0170]

+1