Introduce CONFIG_PHYTEC_K3_DDR_PATCH to make DDR timing patch code
optional for PHYTEC K3 boards. This allows better control over which
boards receive DDR timing patches, rather than compiling the code for
all boards with K3_DDRSS enabled.

Also enable the feature by default for PHYCORE_AM62X_R5.

Signed-off-by: Garrett Giordano <ggiordano@phytec.com>
Reviewed-by: Wadim Egorov <w.egorov@phytec.de>

Introduce fdt_apply_ddrss_timings_patch() to allow board code to
override DDR settings in the device tree prior to DDRSS driver probing.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Tested-by: John Ma <jma@phytec.com>

Environment handling code can be reused across all our K3 based SoMs.
Instead of adding the same code for every new SoM, move it to a common
board.c file.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>