The sama5d2 can be fused for one of 9 preset UART iosets. This is then
used by the BootROM for printing the `RomBOOT' header and for the XMODEM
protocol implemented by the SAM-BA monitor. Add two new sama5d2 specific
helpers:

- sama5d2_dbgu_setup_ll for setting up the port with only pinmux and
  master clock as arguments
- sama5d2_resetup_uart_console for resetup of the uart console with
  same pinmux used by the ROM code

The default value, when unfused, is UART_1_IOSET_1 (RX@PD2, TX@PD3),
which are the same ones used on the two sama5d2 board supported so far.

With this change, the DEBUG_LL baudrate is also no longer fixed at 115200,
but instead comes from the CONFIG_BAUDRATE symbol.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

The SAMA5D2 and SAM9X60 both feature generic clocks, which we already
support in barebox proper, but not in PBL. Add PBL support for setting
the parent and enabling them, so we may use it to enable the SDMMC
peripherals in first stage.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Port over the low level initialization for sama5d2 SoCs from
at91bootstrap.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>