AArch32: Miscellaneous fixes in the AArch32 code

This patch makes following miscellaneous fixes:
* pl011_console.S: Fixed the bit mask used to check if the
  transmit FIFO is full or empty.
* smcc_macros.S: Added `_fsxc` suffix while updating the SPSR.
  By default the assembler assumes `_fc` suffix which does not
  update all the fields in SPSR. By adding `_fsxc` suffix all
  the fields gets updated.
* platform_helpers.S: Removed the weak definition for
  `plat_my_core_pos()` as this is a mandatory function which
  needs to be defined by all platforms.

Change-Id: I8302292533c943686fff8d7c749a07132c052a3b
Signed-off-by: Yatharth Kochar <yatharth.kochar@arm.com>