XUart driver accesses status register directly rather than using XUartLite_GetSR

There are quite a few places in the XUartLite driver which access the status register directly rather than calling XUartLite_GetSR which means that the receive error stats don't get updated.

The following functions/macros access the status register directly:

From xuartlite.c:
XUartLite_ResetFifos
XUartLite_IsSending

From: xuartlite_selftest.c
XUartLite_SelfTest

From xuartlite_intr.c:
XUartLite_InterruptHandler - this function is the biggest offender and it even has the InstancePtr as an argument.

I understand the low level functions from xuartlite_l.c/.h not using XUartLite_GetSR, but it would be nice if there were high-level equivalent functions.

From xuartlite_l.h
XUartLite_GetStatusReg
XUartLite_IsReceiveEmpty (goes through XUartLite_GetStatusReg)
XUartLite_IsTransmitFull (goes through XUartLite_GetStatusReg)
XUartLite_IsIntrEnabled (goes through XUartLite_GetStatusReg)

From xuartlite_l.c
XUartLite_SendByte (goes through XUartLite_IsTransmitFull)
XUartLite_RecvByte (goes through XUartLite_IsReceiveEmpty)

Start by tracing XUartLite_GetSR and the direct status-register accesses listed in xuartlite.c, xuartlite_selftest.c, xuartlite_intr.c, xuartlite_l.h, and xuartlite_l.c. Review XUartLite_InterruptHandler first, then compare the other high-level functions and macros. Done means the listed high-level accesses consistently update receive error statistics while the low-level functions remain unchanged.