mtd: cfi: Fix PPB lock status readout

mtd: cfi: Fix PPB lock status readout

According to S26KL512S datasheet [1] and S29GL01GS datasheet [2],
the procedure to read out PPB lock bits is to send the PPB Entry,
PPB Read, Reset/ASO Exit. Currently, the code does send incorrect
PPB Entry, PPB Read and Reset/ASO Exit is completely missing.

The PPB Entry sent is implemented by sending flash_unlock_seq()
and flash_write_cmd(..., FLASH_CMD_READ_ID). This translates to
sequence 0x555:0xaa, 0x2aa:0x55, 0x555:0x90=FLASH_CMD_READ_ID.
However, both [1] and [2] specify the last byte of PPB Entry as
0xc0=AMD_CMD_SET_PPB_ENTRY instead of 0x90=FLASH_CMD_READ_ID,
that is  0x555:0xaa, 0x2aa:0x55, 0x555:0xc0=AMD_CMD_SET_PPB_ENTRY.
Since this does make sense, this patch fixes it and thus also
aligns the code in flash_get_size() with flash_real_protect().

The PPB Read returns 00h in case of Protected state and 01h in case
of Unprotected state, according to [1] Note 83 and [2] Note 17, so
invert the result. Moreover, align the arguments with similar code
in flash_real_protect().

Finally, Reset/ASO Exit command should be executed to exit the PPB
mode, so add the missing reset.

[1] https://www.cypress.com/file/213346/download
    Document Number: 001-99198 Rev. *M
    Table 40. Command Definitions, Nonvolatile Sector Protection
    Command Set Definitions
[2] https://www.cypress.com/file/177976/download
    Document Number: 001-98285 Rev. *R
    Table 7.1 Command Definitions, Nonvolatile Sector Protection
    Command Set Definitions

Fixes: 03deff433e ("cfi_flash: Read PPB sector protection from device for AMD/Spansion chips")
Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Stefan Roese <sr@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>