configs: bcm963158 disable CONFIG_CMD_BOOTEFI_SELFTEST

Configuration option CONFIG_CMD_BOOTEFI_SELFTEST is useful for the
development of the UEFI sub-system. For production it is not needed.

Remove CONFIG_CMD_BOOTEFI_SELFTEST from bcm963158_ram_defconfig.

Suggested-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>