UART_RESET, UART_CLK_RUNNING_MASK, and UART_SMART_IDLE_EN
are defined inn evm.c but not used. Also removes unnecessary
include of serial.h

PHYS_DRAM_1_SIZE is defined in am335x_evm.h but never used.
Signed-off-by: NSteve Sakoman <steve@sakoman.com>