asm_macros: set the default assembly code alignment to 4 byte

asm_macros: set the default assembly code alignment to 4 byte

Assembly routines are usually defined by using "func" and "endfunc":

    func foo
      ...
    endfunc foo

Currently, the "func" macro does not specify ".align" directive
by default.  It causes unaligned instruction under some circumstances.

As far as I tested, this problem happens for GCC 5 or older.  It did
not happen for GCC 6 or newer.  Taking into account that GCC 4.x / 5.x
is still used, make sure that assembly code is at least 4 byte aligned.

[ How to reproduce the problem ]

For example, use GCC 5.3 downloaded from Linaro:
http://releases.linaro.org/components/toolchain/binaries/5.3-2016.05/
aarch64-linux-gnu/gcc-linaro-5.3.1-2016.05-x86_64_aarch64-linux-gnu.tar.xz

Expand mbedtls-2.4.2 to the current directory.

Try the following:

  $ git log --oneline -1
  77544ef Merge pull request #1071 from jeenu-arm/syntax-fix
  $ aarch64-linux-gnu-gcc --version | head -1
  aarch64-linux-gnu-gcc (Linaro GCC 5.3-2016.05) 5.3.1 20160412
  $ make CROSS_COMPILE=aarch64-linux-gnu- PLAT=uniphier \
    TRUSTED_BOARD_BOOT=1 MBEDTLS_DIR=mbedtls-2.4.2
    ( snip build log )
  $ aarch64-linux-gnu-nm build/uniphier/release/bl1/bl1.elf | grep handler
  00000000800088f4 T bl1_fwu_smc_handler
  00000000800084c8 T bl1_smc_handler
  000000008000a6e0 t _panic_handler
  000000008000a8e0 W plat_error_handler
  000000008000a8e8 W plat_panic_handler
  000000008000a8d8 W plat_reset_handler
  000000008000a39f T reset_handler
  000000008000a367 t smc_handler
  000000008000a2ef t smc_handler64

You will notice "smc_handler64", "reset_handler", etc. are not properly
aligned.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>