config: remap flags used for Arm platforms

config: remap flags used for Arm platforms

RTE_ARCH_xx flags are used to distinguish platform architectures.
These flags can be used to pick different code paths for different
architectures at compile time.
For Arm platforms, there are 3 flags in use: RTE_ARCH_ARM,
RTE_ARCH_ARMv7 and RTE_ARCH_ARM64.
RTE_ARCH_ARM64 is for 64-bit aarch64 platforms,
and RTE_ARCH_ARM & RTE_ARCH_ARMv7 are for 32-bit platforms.
RTE_ARCH_ARMv7 is for ARMv7 platforms as its name suggested.

The issue is meaning of RTE_ARCH_ARM is not clear enough.
Because no info about platform word length is included in the name.
To make the flag names more clear, a naming scheme is proposed.

RTE_ARCH_ARM (all Arm platforms)
    |
    +----RTE_ARCH_32 (New. 32-bit platforms of all architectures)
    |        |
    |        +----RTE_ARCH_ARMv7 (ARMv7 platforms)
    |        |
    |        +----RTE_ARCH_ARMv8_AARCH32 (aarch32 state on aarch64 machine)
    |
    +----RTE_ARCH_64 (64-bit platforms of all architectures)
             |
             +----RTE_ARCH_ARM64 (64-bit Arm platforms)

RTE_ARCH_32 will be explicitly defined for 32-bit platforms.

To fit into the new naming scheme, current usage of RTE_ARCH_ARM in
project is mapped to (RTE_ARCH_ARM && RTE_ARCH_32).

Matching flags for other architectures are:
RTE_ARCH_X86
    |
    +----RTE_ARCH_32
    |        |
    |        +----RTE_ARCH_I686
    |        |
    |        +----RTE_ARCH_X86_X32
    |
    +----RTE_ARCH_64
             |
             +----RTE_ARCH_X86_64

RTE_ARCH_PPC_64 ---- RTE_ARCH_64

Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>