configs: am62x_evm_*: Correct SPI configuration option

In f422c4bec the configuration option to support s28hs512t SPI flashes
was changed from CONFIG_SPI_FLASH_S28HS512T to CONFIG_SPI_FLASH_S28HX_T
to support the wider family. Follow this change in the AM62x EVM
configurations.

Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
2 files changed