kernel: serial: amba-pl011: avoid SBSA UART accessing DMACR register

A flaw was found in the Linux kernel’s AMBA-PL011 serial driver used on ARM Server Base System Architecture platforms. The existing stoprx operation shared between generic SBSA UARTs and AMBA-PL011 UARTs invoked pl011dmarxstop, which attempts to access the DMA Control Register DMACR. SBSA generic...