mcp6x_spi.c: Refactor singleton states into reentrant pattern

Move global singleton states into a struct and store within
the bitbang_spi_master data field for the life-time of the driver.

This patch also drops `mcp6x` and `mcp` prefixes from spi data
struct members.

This is one of the steps on the way to move spi_master data
memory management behind the initialisation API, for more
context see other patches under the same topic "register_master_api".

BUG=b:185191942
TEST=builds

Change-Id: Ia02c1cb9d36fb7b15bb7e09b769d8969c08c2bd5
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/54994
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
1 file changed