Remove HMI10 board support

Recent changes caused that the HMI10 board now is included in the
boards built by MAKEALL, which revealed that compilation for this
board has been broken for a long time:

ps2ser.c: In function 'ps2ser_init':
ps2ser.c:155: error: 'UART_LCR' undeclared (first use in this function)
ps2ser.c:155: error: (Each undeclared identifier is reported only once
ps2ser.c:155: error: for each function it appears in.)
ps2ser.c:156: error: 'UART_DLL' undeclared (first use in this function)
ps2ser.c:157: error: 'UART_DLM' undeclared (first use in this function)
ps2ser.c:159: error: 'UART_IER' undeclared (first use in this function)
ps2ser.c:160: error: 'UART_MCR' undeclared (first use in this function)
ps2ser.c:161: error: 'UART_FCR' undeclared (first use in this function)
ps2ser.c:162: error: 'UART_FCR_ENABLE_FIFO' undeclared (first use in this function)
ps2ser.c:166: error: 'UART_LSR' undeclared (first use in this function)
ps2ser.c: In function 'ps2ser_putc':
ps2ser.c:198: error: 'UART_LSR' undeclared (first use in this function)
ps2ser.c:200: error: 'UART_TX' undeclared (first use in this function)
ps2ser.c: In function 'ps2ser_getc_hw':
ps2ser.c:224: error: 'UART_LSR' undeclared (first use in this function)
ps2ser.c:225: error: 'UART_RX' undeclared (first use in this function)
ps2ser.c: In function 'ps2ser_interrupt':
ps2ser.c:293: error: 'UART_IIR' undeclared (first use in this function)

The board is orphaned, and AFAICT has reached EOL.
Drop support for it.

Signed-off-by: Wolfgang Denk <wd@denx.de>