plat/arm : update BL size macros to give BL1 and BL2 more space for TBB

For Trusted Board Boot, BL1 RW section and BL2 need more space to
support the ECDSA algorithm. Specifically, PLAT_ARM_MAX_BL1_RW_SIZE
is increased on ARM platforms.

And on the Juno platform:
    - BL2 size, PLAT_ARM_MAX_BL2_SIZE is increased.
    - SCP_BL2 is loaded into the space defined by BL31_BASE ->
      BL31_RW_BASE. In order to maintain the same size space for
      SCP_BL2,PLAT_ARM_MAX_BL31_SIZE is increased.

Change-Id: I379083f918b40ab1c765da4e71780d89f0058040
Co-Authored-By: David Cunado <david.cunado@arm.com>
Signed-off-by: Qixiang Xu <qixiang.xu@arm.com>