arm64/mm: Allow __create_pgd_mapping() to propagate pgtable_alloc() errors

arch_add_memory() is used to hotplug memory into a system but as a part
of its implementation it calls __create_pgd_mapping(), which uses
pgtable_alloc() in order to build intermediate page tables. As this path
was initally only used during early boot pgtable_alloc() is designed to
BUG_ON() on failure. However, in the event that memory hotplug is
attempted when the system's memory is extremely tight and the allocation
were to fail, it would lead to panicking the system, which is not
desirable. Hence update __create_pgd_mapping and all it's callers to be
non void and propagate -ENOMEM on allocation failure to allow system to
fail gracefully.

But during early boot if there is an allocation failure, we want the
system to panic, hence create a wrapper around __create_pgd_mapping()
called early_create_pgd_mapping() which is designed to panic, if ret
is non zero value. All the init calls are updated to use this wrapper
rather than the modified __create_pgd_mapping() to restore
functionality.

Fixes: 4ab2150 ("arm64: Add memory hotplug support")
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Chaitanya S Prakash <chaitanyas.prakash@arm.com>
Signed-off-by: Linu Cherian <linu.cherian@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: Chaitanya S Prakash