Adjust written value for SDIDMAX to match mttp register diagrams

[grg-haas]

Registers 1 and 2, for 32-bit and 64-bit mttp respectively, show a 6-bit field for SDID (WARL). However, the text describing SDIDMAX specifies that the 32-bit value is 8 and the 64-bit value is 16, which both clearly cannot fit into a 6-bit field. Clarify the text to note that SDIDMAX should be 6 for both the 32-bit and 64-bit mttp registers.

[rsahita]

thanks!