1. This removes hardcoded iomux/clk/addr configuration for debug uart,
provides possibility (as a workaround, till that information isn't
provided via DT) to set this configuration during compile time via
IMX_DEBUG_UART build flag.

Also for Colibri i.MX8QXP different pinmux configuration is applied
for UART3, FLEXCAN2_RX/TX pads are muxed to ADMA_UART3_RX/TX.

2. Having DEBUG_CONSOLE enabled without enabling DEBUG_CONSOLE_A35
doesn't make sense (since UART pinmux/clock configuration is applied
for UART only when DEBUG_CONSOLE_A35 is enabled. Check similar commit
for i.MX8QM 98a69dfd4a("plat: imx: imx8qm: apply clk/pinmux
configuration for DEBUG_CONSOLE")).

Usage:
$ make PLAT=imx8qx IMX_DEBUG_UART=3 DEBUG_CONSOLE=1 bl31

Signed-off-by: Igor Opaniuk <igor.opaniuk@gmail.com>
Change-Id: I5d04939b2e8ee1a5f4b2f3c6241977d3c6e91760