powerpc/uaccess: Remove {allow/prevent}_{read/write/read_write}_{from/to/}_user()

powerpc/uaccess: Remove {allow/prevent}_{read/write/read_write}_{from/to/}_user()

The six following functions have become simple single-line fonctions
that do not have much added value anymore:
- allow_read_from_user()
- allow_write_to_user()
- allow_read_write_user()
- prevent_read_from_user()
- prevent_write_to_user()
- prevent_read_write_user()

Directly call allow_user_access() and prevent_user_access(), it doesn't
reduce the readability and it removes unnecessary middle functions.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/70971f0ba81eab742a120e5bfdeff6b42d08fd98.1766574657.git.chleroy@kernel.org