arm: dts: brcp1: Move SPL partition to offset 0x8000 in SPI flash

arm: dts: brcp1: Move SPL partition to offset 0x8000 in SPI flash

The ROM code of Xilinx Zynq searches the boot flash for a "BootROM header"
at increments of 32k (0x8000), beginning with 0x0000 for a
configuration without authentication and beginning with 0x8000
for a configuration with authentication. [1]

Move the offset of the SPL partition on the brcp1 board to 0x8000
so that both cases are the same, e.g. a board that is configured
without authentication can boot an SPL partition with or without
authentication.

[1] Zynq 7000 TRM, section 6.3 "BootROM Code"

Signed-off-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/20251029092252.115582-1-wolfgang.wallner@br-automation.com