powerpc/kuap: KUAP enabling/disabling functions must be __always_inline

Objtool reports following warnings:

  arch/powerpc/kernel/signal_32.o: warning: objtool:
    __prevent_user_access.constprop.0+0x4 (.text+0x4):
    redundant UACCESS disable

  arch/powerpc/kernel/signal_32.o: warning: objtool: user_access_begin+0x2c
    (.text+0x4c): return with UACCESS enabled

  arch/powerpc/kernel/signal_32.o: warning: objtool: handle_rt_signal32+0x188
    (.text+0x360): call to __prevent_user_access.constprop.0() with UACCESS enabled

  arch/powerpc/kernel/signal_32.o: warning: objtool: handle_signal32+0x150
    (.text+0x4d4): call to __prevent_user_access.constprop.0() with UACCESS enabled

This is due to some KUAP enabling/disabling functions being outline
allthough they are marked inline. Use __always_inline instead.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/ca5e50ddbec3867db5146ebddbc9a1dc0e443bc8.1689091022.git.christophe.leroy@csgroup.eu