tty/serial: altera_uart: use more informative labels in /proc/interrupts

Before:

root@stretch:~# cat /proc/interrupts
...
 40:        123          0     GIC-0  72 Level     altera_uart
 41:          9          0     GIC-0  73 Level     altera_uart

After:

root@stretch:~# cat /proc/interrupts
...
 40:          6          0     GIC-0  72 Level     ff200100.fpga-uart0
 41:         28          0     GIC-0  73 Level     ff200200.fpga-uart1

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>