am335x_evm: Enable use of UART{1,2,3,4,5}

Add targets of am335x_evm_uart{1,2,3,4,5} to have serial input/output on
UART{1,2,3,4,5} for use with the Beaglebone RS232 cape, am335x_evm
daughterboard, and other custom configurations.

Modify target for am335x_evm to include SERIAL1 and CONS_INDEX=1
options in order to clarify UART selection requirements.

Signed-off-by: Andrew Bradford <andrew@bradfordembedded.com>