When building kernel for xtensa cores with big cache lines (e.g. 128
bytes or more) __loop_cache_all and __loop_cache_page may generate
assembly instructions with immediate fields that are too big. This
results in the following build errors:

  arch/xtensa/mm/misc.S: Assembler messages:
  arch/xtensa/mm/misc.S:464: Error: operand 2 of 'diwbi' has invalid value '256'
  arch/xtensa/mm/misc.S:464: Error: operand 2 of 'diwbi' has invalid value '384'
  arch/xtensa/kernel/head.S: Assembler messages:
  arch/xtensa/kernel/head.S:172: Error: operand 2 of 'diu' has invalid value '256'
  arch/xtensa/kernel/head.S:172: Error: operand 2 of 'diu' has invalid value '384'
  arch/xtensa/kernel/head.S:176: Error: operand 2 of 'iiu' has invalid value '256'
  arch/xtensa/kernel/head.S:176: Error: operand 2 of 'iiu' has invalid value '384'
  arch/xtensa/kernel/head.S:255: Error: operand 2 of 'diwb' has invalid value '256'
  arch/xtensa/kernel/head.S:255: Error: operand 2 of 'diwb' has invalid value '384'

Add parameter max_immed to these macros and use it to limit values of
immediate operands. Extract common code of these macros into the new
macro __loop_cache_unroll.

Cc: stable@vger.kernel.org
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>