board: ti: am62x: evm: Include necessary header files

At the time of compilation evm.c gives below warning for implicit
declaration of enable_caches, to mitigate this include cpu_func.h.

board/ti/am62x/evm.c: In function ‘spl_board_init’:
board/ti/am62x/evm.c:90:9: warning: implicit declaration of function ‘enable_caches’ [-Wimplicit-function-declaration]
90 |         enable_caches();

Signed-off-by: Nikhil M Jain <n-jain1@ti.com>