ARM64 / ACPI: Get RSDP and ACPI boot-time tables

As we want to get ACPI tables to parse and then use the information
for system initialization, we should get the RSDP (Root System
Description Pointer) first, it then locates Extended Root Description
Table (XSDT) which contains all the 64-bit physical address that
pointer to other boot-time tables.

Introduce acpi.c and its related head file in this patch to provide
fundamental needs of extern variables and functions for ACPI core,
and then get boot-time tables as needed.
  - asm/acenv.h for arch specific ACPICA environments and
    implementation, It is needed unconditionally by ACPI core;
  - asm/acpi.h for arch specific variables and functions needed by
    ACPI driver core;
  - acpi.c for ARM64 related ACPI implementation for ACPI driver
    core;

acpi_boot_table_init() is introduced to get RSDP and boot-time tables,
it will be called in setup_arch() before paging_init(), so we should
use eary_memremap() mechanism here to get the RSDP and all the table
pointers.

FADT Major.Minor version was introduced in ACPI 5.1, it is the same
as ACPI version.

In ACPI 5.1, some major gaps are fixed for ARM, such as updates in
MADT table for GIC and SMP init, without those updates, we can not
get the MPIDR for SMP init, and GICv2/3 related init information, so
we can't boot arm64 ACPI properly with table versions predating 5.1.

If firmware provides ACPI tables with ACPI version less than 5.1,
OS has no way to retrieve the configuration data that is necessary
to init SMP boot protocol and the GIC properly, so disable ACPI if
we get an FADT table with version less that 5.1 when acpi_boot_table_init()
called.

CC: Catalin Marinas <[email protected]>
CC: Will Deacon <[email protected]>
CC: Lorenzo Pieralisi <[email protected]>
Tested-by: Suravee Suthikulpanit <[email protected]>
Tested-by: Yijing Wang <[email protected]>
Tested-by: Mark Langsdorf <[email protected]>
Tested-by: Jon Masters <[email protected]>
Tested-by: Timur Tabi <[email protected]>
Tested-by: Robert Richter <[email protected]>
Acked-by: Robert Richter <[email protected]>
Acked-by: Olof Johansson <[email protected]>
Acked-by: Grant Likely <[email protected]>
Signed-off-by: Al Stone <[email protected]>
Signed-off-by: Graeme Gregory <[email protected]>
Signed-off-by: Tomasz Nowicki <[email protected]>
Signed-off-by: Hanjun Guo <[email protected]>
Signed-off-by: Will Deacon <[email protected]>

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