board:ls2080ardb: Update execution of config_board_mux

Function config_board_mux() reads env variable 'hwconfig' which is
only available after relocation for QSPI boot. Move calling
config_board_mux() to misc_init_r().

Signed-off-by: Santan Kumar <santan.kumar@nxp.com>
[YS: Revise commit message]
Reviewed-by: York Sun <york.sun@nxp.com>