drivers: serial: pl011: Introduce macros to separate device-dependent code

Introduce the `COMPAT_SPECIFIC_...` macros to determine the function name
from the compatible name.
These macros allow the isolation of device-dependent code in a generic way.

For example, if the compatible name is `ambiq,uart`,
The `COMPAT_SPECIFIC_DEFINE` macro is replaced by `AMBIQ_UART_DEFINE`.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>