arm64: realm: Fix PTE_NS_SHARED for 52bit PA support

With LPA/LPA2, the top bits of the PFN (Bits[51:48]) end up in the lower bits
of the PTE. So, simply creating a mask of the "top IPA bit" doesn't work well
for these configurations to set the "top" bit at the output of Stage1
translation.

Fix this by using the __phys_to_pte_val() to do the right thing for all
configurations.

Tested using, kvmtool, placing the memory at a higher address (-m <size>@<Addr>).

 e.g:
 # lkvm run --realm -c 4 -m 512M@@128T -k Image --console serial

 sh-5.0# dmesg | grep "LPA2\|RSI"
[    0.000000] RME: Using RSI version 1.0
[    0.000000] CPU features: detected: 52-bit Virtual Addressing (LPA2)
[    0.777354] CPU features: detected: 52-bit Virtual Addressing for KVM (LPA2)

Fixes: 399306954996 ("arm64: realm: Query IPA size from the RMM")
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>