powerpc/pseries/papr-sysparm: use u8 arrays for payloads

Some PAPR system parameter values are formatted by firmware as
nul-terminated strings (e.g. LPAR name, shared processor attributes).
But the values returned for other parameters, such as processor module
info and TLB block invalidate characteristics, are binary data with
parameter-specific layouts. So char[] isn't the appropriate type for
the general case. Use u8/__u8.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Fixes: 905b9e48

 ("powerpc/pseries/papr-sysparm: Expose character device to user space")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240202-papr-sysparm-ioblock-data-use-u8-v1-1-f5c6c89f65ec@linux.ibm.com