target/arm: Remove useless TARGET_BIG_ENDIAN check in armv7m_load_kernel()

target/arm: Remove useless TARGET_BIG_ENDIAN check in armv7m_load_kernel()

Arm system emulation targets always have TARGET_BIG_ENDIAN clear, so
there is no need to have handling in armv7m_load_kernel() for the
case when it is defined.  Remove the unnecessary code.

Side notes:
 * our M-profile implementation is always little-endian (that is, it
   makes the IMPDEF choice that the read-only AIRCR.ENDIANNESS is 0)
 * if we did want to handle big-endian ELF files here we should do it
   the way that hw/arm/boot.c:arm_load_elf() does, by looking at the
   ELF header to see what endianness the file itself is

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220823160417.3858216-2-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>