firmware/psci: Fix MEM_PROTECT_RANGE function numbers

PSCI v1.1 offers 32-bit and 64-bit variants of the MEM_PROTECT_RANGE
call using function identifier 20.

Fix the incorrect definitions of the MEM_PROTECT_CHECK_RANGE calls in
the PSCI UAPI header.

Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Fixes: 3137f2e6 ("firmware/psci: Add debugfs support to ease debugging")
Signed-off-by: Will Deacon <will@kernel.org>