LPC845: Fields in SPI.STAT are write-only; should be readable

[hannobraun]

According to the user manual, they following fields in SPI.STAT can be read and can be cleared by writing 1:

• RXOV
• TXUR
• SSA
• SSD

In the SVD file, all of them are marked as write-only.

[hannobraun]

I just discovered more fields for which this problem exists. Updated title and description.