Align LOG_* messages with the upstream style - remove trailing punctuation

[JanMatCodasip]

The upstream OpenOCD style asks that log messages (printed by LOG_* and LOG_TARGET_* macros) do not end with any punctuation mark like . or !.

See the C Style Guide which says: Do not use a period or exclamation mark at the end of a message.

The task is to:

• Remove the trailing punctuation in all log messages in src/target/riscv/*,
• except for messages that consist of multiple sentences.