firmware: dcdbas: include linux/io.h

memremap() is declared in linux/io.h, not in asm/io.h, so we should
include that header to avoid build errors:

drivers/platform/x86/dcdbas.c: In function 'dcdbas_check_wsmt':
drivers/platform/x86/dcdbas.c:572:15: error: implicit declaration of function 'memremap'; did you mean 'ioremap'? [-Werror=implicit-function-declaration]
  eps_buffer = memremap(eps->smm_comm_buff_addr, remap_size, MEMREMAP_WB);
               ^~~~~~~~
               ioremap
drivers/platform/x86/dcdbas.c:572:61: error: 'MEMREMAP_WB' undeclared (first use in this function)
  eps_buffer = memremap(eps->smm_comm_buff_addr, remap_size, MEMREMAP_WB);
                                                             ^~~~~~~~~~~
drivers/platform/x86/dcdbas.c:572:61: note: each undeclared identifier is reported only once for each function it appears in
drivers/platform/x86/dcdbas.c: In function 'dcdbas_exit':
drivers/platform/x86/dcdbas.c:748:3: error: implicit declaration of function 'memunmap'; did you mean 'vm_munmap'? [-Werror=implicit-function-declaration]

Fixes: 12c956c4 ("firmware: dcdbas: Add support for WSMT ACPI table")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>