configs: am62: Add configs for enabling ETHBOOT in R5SPL

Add configs for enabling ETHBOOT in R5SPL.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Chintan Vankar <c-vankar@ti.com>